Little Lotz
Um....
Say I were to go to this website....
http://www.planetrenders.net/
That site has a ton of renders, and I use them often. They put them up there for anyone to use. Frankly, if I am going to use a render of Sonic the Hedgehog and I have to ask Sega....I HIGHLY doubt they would respond to me. They've got better things to do than answer a question from a little graphic artist.
Also, the c4ds are put up there for people to use, or else they would not be added to the site, now would they?
If the site states you can take their images and use them without asking permission (otherwise: free to take) then yes you can take them.
No they would probably not respond to you, unless you were a little graphic artist from a big company. But gaia is a big company (not sure if they are a company or organisation per say) and they could possibly get in trouble for allowing you to "sell" copyrighted material. Will gaia freak out on you for using something you don't own? Probably not unless you were reported for it. But you still should try and avoid using what you don't own as much as possible.
@le fair: If someone on deviantart was making a significant amount of money off a copyrighted character, and they got noticed by the copyright holder then they could ask deviantart to close their account, or they may even take the user to court. Does anyone on deviantart make enough money for the company to aactueally take legal action? Nope, so they won't complain.
It is illegal though, it is called copyright infringement.
@~Silantre~:
You took the photo therefore you own the photo and can do with it as you wish.
@hikArU_onzE: Yes you can sell your self made banners here. Just try not to use images that you don't own in the image.
whee I just felt like answering some questions