The tell is usually in the offer itself. A genuine local cash buyer can show proof of funds and name a specific closing lawyer right away; a lead-generation site typically needs to "match you with a buyer" first, which means your information gets shopped around before any real offer appears.
Wholesaling, where the site assigns its contract to another buyer for a fee before closing, is legal in Saskatchewan but should be disclosed, and a seller who does not realize it is happening can end up accepting a lower price than the eventual real buyer actually pays.
A listing on the open market, priced correctly, almost always nets more than an unsolicited cash offer from a site you found on Google. Get your hand-reviewed valuation from Joel Dyck.