Yeah , as a newb to this , i tend to lack confidence in the survey method , seeing as : i never wanted to buy anything through a surprise guerrilla survey ,and ,nowadays ,i just immediately delete anything that i get that's locked this way.
Apparently there are a teeny tiny amount of people that don't mind buying something in the hopes of getting a password to unzip a "free" keygen. I imagine , juveniles that have access to parents bank card?
A more legit approach that these people use can be : just giving the desired file in the torrent , and including a text file in the download with url's promoting other ventures.
Torrent sites themselves tend to have "low rent" looking ad banners to support their upkeep , so , i doubt any torrent sites do any sort of partner program / ad revenue sharing programs.