I don't know that there is any precedent set for governing design/creative sourcing sites, but I have a few notions about Crowdspring.com. This site panders to "cheap" clients who troll for new logos from hundreds of artists and writers.
I have entered a few of their contests to "hone" my creative talents. In 2 of the contests, I am the only entrant to receive a top, 5-star rating after heeding direction from the buyer in my "Comment" section. I seemed poised for the wins, only to be "beaten out" by some entrant who had only submitted 1 or 2 poor quality designs. It is my contention that their are Buyers who team up with their friends or colleagues. The [incognito] colleague enters a [lame, MS Word generated] logo somewhere in the competition. Meanwhile the buyer is feeding me detailed, multiple revision instructions until I get the design "perfect". The contest closes, and then crickets.
The next thing you know, I'm being notified by CS that the "lame" design won the contest even though I had the only 5-star entries and submitted 13 revisions to suit the buyer. It is my theory, the buyer then makes the payment to the colleague with the "winning" entry, who turns around and returns it right back to him. Thereby the buyer gets HUNDREDS of designs from artists for free that he can have anyone with a basic knowledge of Adobe Illustrator or CorelDraw, rebuild/plagiarize.
I have also submitted designs, where it is obvious the buyer instructed another artist to copy my design but add a small change at the eleventh hour, but doesn't share the same instructions with the other participants. The project closes before we can see the new changes and can alter our designs to suit. I suspect Crowdspring has no plan in place to track this kind of reprehensible behavior, nor do they care since they're getting paid. I'm just waiting to find a "version" of a non-winning logo of mine pop up on the buyer's website...