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Entrusting your SEO to an agency is a decision that commits a company for several months, sometimes even years. A good agency sustainably grows organic traffic and revenue. A bad one wastes time and budget, and can even penalize your site. Between promises of top rankings and quotes that are difficult to compare, here are the concrete criteria for choosing the right SEO agency, the questions to ask before signing, and the red flags to watch out for.
Why hire an SEO agency?
SEO requires a diverse set of skills that few companies have in-house: technical development and architecture, optimized copywriting, data analysis, and link strategy. An SEO agency provides a team of experts, professional tools, and the perspective gained from working on dozens of sites. Most importantly, it helps you avoid costly mistakes, such as a poorly planned migration or a content strategy that cannibalizes existing pages.
In 2026, the role of an SEO agency has expanded. Search is no longer limited to Google: a growing number of users are asking their questions directly to AI search engines. Choosing an SEO agency therefore also means choosing a partner that will make your brand visible in these new types of answers.
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Criteria for choosing the right SEO agency
Comprehensive expertise across the 3 pillars of SEO
SEO is based on three inseparable pillars. The technical SEO ensures that the site is fast, crawlable, and correctly indexed. The content addresses user search intent, page by page. The popularity strengthens the site's authority through netlinking and mentions. An agency that only masters one of these levers will not be able to build an effective long-term SEO strategy. Some add a fourth pillar, user experience, which determines the conversion of the traffic gained.
An SEO audit before any proposal
A reputable agency does not sell a standard package. They first conduct an SEO audit : they analyze your site, your rankings, your competitors, and your market, then propose a prioritized action plan. Be wary of a quote sent without anyone having looked at your site.
Concrete and verifiable results
Ask for case studies with hard numbers: organic traffic growth, number of keywords on the first page, and revenue generated. Also, verify that the agency practices what it preaches by checking how it ranks on Google itself.
A white-hat and transparent approach
The abusive SEO techniques (mass buying of low-quality links, duplicate content, keyword stuffing) may provide a quick boost, but they often lead to long-term penalties. A good agency explains its actions, gives you access to data, and documents every recommendation.
A dedicated point of contact and reporting aligned with your goals
The project manager is the person you will work with on a daily basis. Ask who they will be, what their experience is, and how often you will have progress meetings. The SEO reporting must go beyond just rankings: it should cover traffic, conversions, revenue, and share of voice.
An agency that already integrates GEO
This is the deciding factor in 2026. GEO (Generative Engine Optimization) GEO involves getting your brand cited in responses from ChatGPT, Gemini, Perplexity, Claude, or AI Overviews. An SEO agency that doesn't yet have a GEO method will cause you to lose out on the visibility of tomorrow. To evaluate this, see our guide on how to choose your GEO agency.
A broader vision of digital marketing
SEO is more effective when connected to other channels: SEA to quickly test keywords, tracking analytics to accurately measure traffic, and CRM to leverage the leads generated. An agency capable of working with these areas of expertise builds a more cohesive strategy.
SEO agency, freelancer, or in-house team: which should you choose?
ASEO consultant freelance is suitable for small websites and one-off projects with a limited budget, but cannot cover all the pillars of a large site on their own. An in-house team offers in-depth product knowledge, but requires hiring multiple profiles and funding the necessary tools. An SEO agency provides a multidisciplinary team that is immediately operational, with the benefit of experience across many sectors. For an SME or a large corporation looking for sustainable results, this is often the most effective solution.
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Questions to ask before signing with an SEO agency
- What kind of audit do you perform before proposing a strategy?
- Who will be my project manager, and how often will we have progress meetings?
- Is content produced in-house or outsourced?
- How do you acquire links, and on what types of sites?
- Which metrics will you track in your reporting?
- Do you have a method for visibility in AI search engines?
- Can you show me case studies comparable to my sector?
Red flags that should make you run
- A guarantee of a first-place ranking on Google. No agency controls the algorithm; this promise is a clear sign of a lack of professionalism.
- Results in a few days. SEO is a long-term lever; the first effects generally appear within a few months.
- An abnormally low price for a high volume of links or content, which is often synonymous with poor quality.
- Lack of access to your data : Google Search Console, tracking tools, and a list of acquired links.
- A long-term commitment without an exit clause or written objectives.
How much does an SEO agency cost?
The cost of an SEO agency depends on the size of your site, the competition for your keywords, and the strategies implemented. Three models coexist:monthly support (a recurring fee covering technical aspects, content, and netlinking), one-off projects (audits, migrations, redesigns), and content and link budgets, which are often billed separately. To compare quotes, break down each proposal by the number of days of expertise, the volume of content and links included, and the performance indicators being tracked.
How do you measure the performance of your SEO agency?
Set written objectives from the start and track the following SEO KPIs every month: non-branded organic traffic, strategic keywords in the top 3 and on the first page, conversions and revenue generated from SEO, and now, brand presence in AI search engine responses. Good reporting explains fluctuations and proposes next steps.
datashake, an SEO and GEO agency that ticks all the boxes
Founded by two former employees of Google's European headquarters, datashake is a digital acceleration group based in Paris (16 rue de Bucarest) and New York. The group has supported over 1,000 advertisers, managed more than €500M in media investment, and brings together over 100 experts. It is a Google Partner Premier, selected for the Google Partners International Growth Program, and is a Meta Business Partner, TikTok Marketing Partner, and Microsoft Advertising Select Partner.
ItsSEO and GEO meets every criterion in this guide point by point:
- An audit of over 100 checkpoints at the start of every mission, covering technical aspects, semantics, popularity, and visibility in AI search engines.
- The 3 pillars mastered in-house : technical optimization (load times, structured data, architecture), end-to-end editorial strategy, netlinking and digital PR, as well as CRO to turn traffic into conversions.
- A proven GEO method, with an in-house developed monitoring tool that tracks brand presence in ChatGPT, Perplexity, Bing Copilot, and AI Overviews.
- Quantifiable results : on average, organic traffic is tripled and over 45% of strategic keywords reach the top 3 on Google.
Client case studies confirm this. For Rip Curl, the synergy between SEO and SEA delivered a 34% increase in first-position keywords and a 52% increase in organic and paid traffic. For IZAC, optimizing strategic pages generated a 29% increase in first-position keywords and a 15% increase in organic revenue. For Celio, a 38% increase in first-position keywords and a 60% increase in impressions on ChatGPT. Chanel, Société Générale, Qonto, EDF, Europcar, and Ladurée are also among the brands we have supported.
Looking for support with your SEO strategy? Get in touch with usfor a free audit of your SEO and GEO visibility!
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FAQ
What are the 3 types of SEO?
There is technical SEO (performance, indexing, site structure), content or on-page SEO (pages that address search intent), and off-page SEO (popularity, netlinking, mentions). A good SEO agency works on all three in parallel.
What are the 4 pillars of SEO?
In addition to the three classic pillars (technical, content, popularity), user experience is often added, as it influences both visitor behavior and traffic conversion.
What is the average cost of an SEO agency?
There is no single rate: the price depends on the size of the site, the level of competition, and the levers activated. The most reliable approach is to request an audit and then compare quotes based on the volume of expertise, content, and links included.
Which is the best SEO agency?
The best SEO agency is one that meets all the criteria in this guide: an initial audit, mastery of the three pillars, verifiable results, transparency, and the GEO method. datashake meets these criteria, with proven results for brands like Celio, Rip Curl, and IZAC. See also our ranking of the best SEO agencies in Paris.
How long does it take to see results from an SEO agency?
The initial effects of an SEO strategy generally appear within a few months, depending on the state of the site and the level of competition. Regarding GEO, datashake observes an average timeframe of 2 weeks for a brand to start appearing in LLM responses.
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