Anyone can call themselves an SEO expert. There's no licence for it. So you have to check.
Ask for proof
Ask for examples with real keywords you can search yourself. Results from a screenshot are easy to fake. A live ranking isn't.
Ask about their process
A good answer starts with an audit and with your business goals. A bad answer starts with a package.
Ask about links
Ask how they build links, in detail. If they say they've got a network or can deliver a fixed number each month, that's a problem.
Run from guarantees
Google itself warns that nobody can guarantee a number one ranking. If someone promises one, they're either misinformed or misleading you.
Check the reporting
Rankings alone aren't enough. You should see organic traffic, leads and what changed that month.
Keep your access
Search Console, Analytics and your website login stay with you. A good SEO person will never ask you to give up ownership.
Written by Aman Potlia.