There are a number of practices that have become the norm among artists. Art trades. Commissioning. Adopts.
Although it's not as common, it still happens... there's also art wagering. It's exactly as it sounds, you make a bet with someone about something and the wager is art. This used to be common in certain places like ArtBabble. Two people might be so sure of themselves where they say "if X turns out to be true, I will make Y for you". No different from a lot of bets gamers make on YouTube (e.g. a Pokemon YouTuber once said he'd dye his hair pink if the new type announced while Generation 6 was still incoming turned out to be fairy type, since nobody believed it would be true, but it was and he dyed his hair pink, and it was fabulous). The only issue is a lot of sites are harder on this thing called "gambling" than others and, when they're not underactive, will go after anything resembling it because they don't want to encourage crowds of people in the future saying "but we're just having a Xiaolin Showdown". Would that be too much here (and what are your thoughts)?