True, I doubt that manufacturers would be held responsible for the criminal acts of their customers, except in a very few cases. But there have been numerous lawsuits against gun manufacturers and sellers over exactly this issue. Yes. Guns. Intentionally killing people. What a surprise!

Sure, most of the time, the manufacturer isn't found liable. But again, do you really want to have to go to court to defend yourself?

http://www.libraryindex.com/pages/1752/Court-Rulings-on-Firearms-RESPONSIBILITY-HANDGUN-DEATHS.html

Copyright infringement, or violation of publicity rights/trademark aren't necessarily criminal. In fact, I'd guess there are relatively few instances of criminal indictment. Most of those would be against people such as Kim Dotcom or founders of Pirate Bay. However, the number of civil actions against infringers is likely enormous.

So:

Your customer does something to anger a copyright holder and gets sued. Then that customer names you as third party to the suit because they reasonably believed you had permission from that copyright holder to use their IP.

No intentional infringement necessary.

ETA: Since we're talking about the hazards and responsibilities of placing products in the Renderosity marketplace, the laws of the US are relevant.

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