When watch dealers are selling Rolex and AP and all those brands, are they real? They’re on YouTube showing papers and boxes but could it still be fake?

I’m so confused by the gray market, I don’t understand how they’re so many watch dealers who don’t work real jobs, just buy and sell watches and ship them out to people through Facebook marketplace or eBay or telegram! Idk how a regular guy can start getting access to all these brands and high end watches, how is that even possible? These dudes have less than 500 instagram followers , selling Rolex,Cartier & AP ! Where are they getting the money from? What are the profit margins like for these guys? Are they just finding the right buyer and overcharging ?