So I was just looking over the rules of the Batman v. Superman contest and rule #2 drew my attention:
#2. Designs must be free or they will not count as valid entries and will be removed from the site.
Removed from the site? Since when were priced designs removed from the site? Am I misunderstanding something?
Hi @caitlin_le
I believe they meant to say removed from the contest. I am going to double check on this right now for you 
…perhaps because you cant sell something that is protected by copyright ?? humm… do you think you can make money with batman/superman DC IP ? really ?
a number of company are TOLERANT and let you exchange protected content IF they are FREE … but if you make money with their IP, they can become angry… (think DMCA, advocate, pursuit… etc )
I checked in @caitlin_le and it basically falls in line with what @fantasygraph was saying. Staff does there best policing uploads for IP infringement, also anything uploading directly for a contest that is against Pinshapes content policy cant be accepted. Hope that helps 