You tell a legit digital marketing SEO agency from a retainer seller by asking for proof that connects their work to measurable outcomes: organic traffic growth, keyword ranking movement, and conversions, not just a list of tasks completed each month. A legitimate agency ties every action to a result it can show you in Google Search Console or Analytics, and it will share case studies from comparable businesses before you sign anything. A retainer-focused agency, by contrast, prioritises contract length and activity reports over evidence of actual progress.
The clearest early test is whether an agency can show you a case study from a business in a comparable niche or market, with real traffic and ranking data over a defined period. If the answer is a deck full of logos and no numbers, that is a signal worth taking seriously. In South Africa, SEO retainers typically range from R5,000 to R30,000 per month in 2026, and the price alone tells you nothing about whether the agency will deliver.
Here are the concrete signals that separate a legitimate agency from one that is simply good at selling contracts:
- A legit agency shares anonymised or named case studies showing traffic growth or ranking movement before you commit.
- Their own website ranks for competitive terms in their market, not just their brand name.
- They describe their process: technical audit, on-page optimisation, link acquisition, content planning, not just monthly deliverables.
- They set realistic timelines, typically three to six months for meaningful organic traffic movement.
- They have access to your Google Search Console and Analytics from day one, because real SEO is grounded in your site’s own data.
Bad agencies keep you busy reading reports. Monthly summaries that list “published 4 blog posts” or “built 12 links” without showing ranking or traffic change are a red flag. A good agency connects every action to a metric you can verify. If rankings are moving but revenue is not, ask which ranking improvements actually drove enquiries or conversions in the last quarter. An agency that cannot answer that question clearly is ranking you for low-intent keywords that do not move your business forward.
Web SEM, a Cape Town SEO agency founded in 2008, ranks for competitive SEO-related terms in its own market. That is a verifiable signal of technical competence, and it is the same standard you should apply to any agency you consider. If an agency cannot rank its own site, no amount of polished proposals changes that fact. Ask to see their Search Console data, ask what they would do in the first 90 days, and ask what happens to your rankings if you stop paying. The answers will tell you everything you need to know.