Choosing a SEA Marketing Agency: Selection Criteria

You’re about to hire a SEA marketing agency (SEA, meaning Search Engine Advertising), but you do not want to take a gamble. I get that. In our world, you see two extremes far too often: agencies that mostly “shuffle” campaigns around, and agencies that talk about strategy but forget that your data, your tracking, and your landing pages also need to be right.

In this article, I’ll help you choose an agency based on what really matters. Not on gut feeling. Not on pretty decks. But on a measurable approach, clear execution, and smart control. We use your current situation as the starting point, so you immediately know what your next step should be.

1) Start with your goal, not their approach

A good choice starts with a clear question. What do you want to buy with SEA?

• Do you want more suitable enquiries through forms?
• Do you want more calls with a shorter sales cycle?
• Do you want qualified leads at a specific point in the funnel?
• Do you want more value per conversion, for example through order value or contract value?

Why this matters so much: a SEA marketing agency can be technically strong and still optimise the wrong things if the conversion goals do not match your real revenue. Measurement strategy is therefore not an afterthought. It is the foundation.

What you need to define upfront

Before you ask for proposals, you should have at least this internally, ideally in one document:

1. Conversions you do want to optimise for (for example enquiry, call, or a qualifying step in your lead process).
2. Conversion variants: what is primary for bidding, and what do you use for insight only?
3. Conversion timing: are conversions fast (same day) or longer (several weeks)?
4. Data limitations: does your tracking work reliably, or are you still unsure about it?

With that input, you can compare agencies on approach, not on promises.

2) Selection criteria you can test right away

You are going to assess a SEA marketing agency. Not on who they are, but on how they work. Here are criteria you can test concretely during an intake, audit, or workshop.

A) Tracking and conversion measurement strategy, down to the bone

A strong agency does not just talk about ads. They talk about conversion goals, conversion quality, and what happens if your conversion goals change.

Look at three things:

• Conversion goals and bidding: which conversion actions are primary for bidding, and why?
• Measurement accuracy: how do they improve conversion measurement when privacy or consent has an impact?
• Changes with discipline: how do they prevent disruption to optimisation when something changes in your account?

Google explicitly states that when making meaningful changes to conversion goals or bidding goals, you need to account for the impact on Smart Bidding and avoid making drastic changes too often. You also see advice to only implement changes once you understand the effect and your budgets and goals are aligned. (support.google.com)

There is also Enhanced Conversions, designed to improve the accuracy of conversion measurement and better support bidding, with matching based on customer data you provide. (support.google.com)

Practical test question you can ask the agency:

• “If we want to change our primary conversion action (for example from ‘form started’ to ‘form submitted’ or to a qualifying step), how do you plan that transition, and how do you reduce performance risk during the learning period?”

B) Landing pages and ad experience, no separate campaign islands

You can optimise a lot in Search ads, but if the landing page does not match the search intent, in practice you are paying for frustration. Google also has guidance on landing pages and navigation, and on the importance of a good user experience after a click. (blog.google)

What you want to hear from the agency:

• They connect the ad message to a specific page, not to “a homepage and success”.
• They check whether your enquiry flow works, including speed and form logic.
• They have a test plan for CRO, without it taking months.

C) Campaign status: a structure that stays scalable

You do not need an overly complex maze of campaign components. But you do want a structure you can manage:

• Campaigns by goal and intent, so you do not optimise everything at once.
• Ad groups and keywords that align logically with your landing pages.
• Negative keywords to reduce waste early.
• A process to review search terms for quality, not just volume.

Test question:

• “How do we organise the account so we can scale up without having to start over every time because goals, pages, or categories are mixed together?”

D) Bidding and conversion goals: value-based thinking, but practical

In many accounts, it only becomes clear after months that people have been optimising for the wrong conversions. Good agencies make it concrete:

• They define whether you optimise for conversions, CPA (Cost Per Acquisition or Cost Per Action, depending on what you mean), or ROAS (Return on Ad Spend) with conversion value.
• They explain which conversion actions fall under the same bidding logic.
• They ensure you have enough data for bidding to learn meaningfully.

Google, for example, documents best practices around conversion goals and warns that changing goals or goals tied to Smart Bidding can have an impact. (support.google.com)

Test question:

• “Which conversion actions do you use as primary, and how do you make sure we do not shift during optimisation toward ‘well-measured’ but ‘not valuable’ actions?”

3) Pricing models: what makes sense and what to watch out for

Pricing often says something about how the agency is managed. Not about quality itself, but about behaviour. Pay attention to the combination of model, scope, and governance.

Common pricing structures

• Hourly rate or project fee for a fixed scope (audit, implementation, landing page improvement).
• Monthly retainer for ongoing campaign management.
• Management fee as a percentage of ad spend.
• Performance fee tied to KPIs (for example CPA or Cost Per Lead), sometimes with caps.

What you should check with each model:

• What is included? Think account monitoring, keyword research, negatives, ad testing, landing page feedback, reporting, tracking support.
• What is on your side? Creative, development, data, quote handling, CRM follow-up.
• How do they report? Not just spend and clicks. You want to know: which conversion steps work, and why.
• Who decides on budget and structural changes? With clear rules.

Trade-off to be aware of

With a percentage fee, there can be a natural incentive to increase budget. That is not automatically bad, but you want them to justify decisions with conversion quality and margin logic. With a fixed retainer, there can be an incentive to “manage efficiently” with less optimisation depth. That is why scope, governance, and KPI definition are so important.

A mature agency asks questions like this back to you as well. If they only say “let’s do this” without rules of the game, that is a signal.

4) Evaluation process: how to avoid regret after three months

You want direction in the first few weeks. Not in the sense of “it has to be perfect right away”, but in the sense of: we know what we are measuring, we know which actions drive things, and we are building a measurable optimisation path.

Week 1 through 4: audit and foundation

Ask for a proposal with a timeline. You will immediately see their maturity from that.

• Tracking check: conversion actions, tags, attribution logic, and where data loss can occur.
• Conversion goal inventory: which are primary, which support insight, and which may need to be cleaned up?
• Account structure review: search terms and ad message by intent.
• Landing page diagnosis: where does the flow break down?
• Test plan: what will we test first and what is the decision rule?

Why this works: you prevent SEA from optimising on noise. Google’s own guidance on conversion goals and their impact on bidding makes it clear that timing and approach matter. (support.google.com)

Week 5 through 8: optimisation with control groups in mind

At this stage, you want to learn, not guess. A mature agency works with:

• Clear KPIs (Key Performance Indicator) such as CVR (Conversion Rate), CPA (Cost Per Acquisition or Cost Per Action), and possibly ROAS (Return on Ad Spend) if you measure conversion value.
• A limited set of changes at once. Otherwise you will not know what had an effect.
• A rhythm for search terms and negative keywords.

Watch out for one trap: too many changes, too little consistency in conversion goals and landing pages. Then you lose the learning context of bidding strategies. Google also warns about disruption caused by too many changes around conversion goals and bidding settings. (support.google.com)

What you should be able to say at the end of the pilot

If after 6 to 8 weeks you still cannot answer:

• Which conversion actions drive bidding?
• Which ad audiences and search intents deliver quality?
• Which landing page sections or steps make or break the conversion?

then it was not a real pilot. It was just campaign management.

5) The right questions for your shortlist meeting

Bring these questions with you. They are sharp enough to protect you, but not so aggressive that you scare the agency off. We want collaboration, not an audit war.

Questions about expertise

• “How do you define primary conversions for bidding, and how do you prevent us from optimising for ‘proxy conversions’ that do not match revenue?”
• “What improvements have you made in conversion measurement in the past, such as Enhanced Conversions, and how do you explain what that changes technically and practically?” (support.google.com)
• “How do you make sure landing pages are functional, usable, and consistent with the ad after the click?” (support.google.com)

Questions about execution

• “What do you do in the first 30 days, in order, and with what priorities?”
• “How do you measure whether a change truly contributes to CVR and CPA, and how do you report that?”
• “How do you decide when we scale up versus pause?”

Questions about collaboration

• “Who is responsible for tracking errors, and how quickly do you resolve them?”
• “What feedback loop do you expect from us for landing pages and CRM follow-up?”
• “Which KPIs do you review with us monthly, and what is the decision rule?”

Conclusion: choose for measurability, not marketing talk

When you choose a SEA marketing agency, you need one thing in order: the chain from search intent to conversion must be logical and remain measurable. For that, you need agency expertise in three places: conversion measurement strategy, account structure, and landing page experience.

Our recommended next step is simple:

1. Write down your conversion goals, and mark what is primary for bidding.
2. Ask each agency for a 30 to 60 day pilot plan, with planning for tracking, conversion goals, campaign structure, and landing page improvements.
3. Assess them on concrete answers and on their willingness to explain limitations honestly.

And yes, you are allowed to laugh at yourself once, because in SEA everyone once started with “we’ll fix it later”. Later is expensive. That is why we prefer to do it now. Do you too?

Contextual extra link (optional): SEA: What Is Search Engine Advertising and How Does It Work?