Art should be kept with the owner even though they're banned.
Even though this is implemented in some way, scammers can and will lie about not owning the texture.
Keeping an eye out for a texture is somewhat hard to do that's why there is a Texture Identification thread.

You can't just take art from people freely unless they donate it or let it go as a free texture instead. Taking art from scammers and putting them in public auctions doesn't seem right.