How to determine if SEO is working?

Track outcomes, not rankings. On the barbershop project I set up GTM click events on the phone number and the booking button before doing anything else, so we'd know whether traffic actually did something.

Search Console gives you impressions, clicks, and which queries you're appearing for. Google Analytics shows behavior and conversions. Rankings alone are vanity. A TOP 3 spot for a keyword nobody clicks is worthless.

The honest signs SEO is working: more clicks from search, more events fired on the site, more calls, more bookings. Compare against the baseline before you started. And give it months, not weeks.