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I agree there, if you print it and or paint it, why not sell it? it is then a custom painted derivative and as long as you state clearly it is unofficial and unlicensed you should be ok, I can't see them knocking on your door. Whether a royalty is owed to the copyright owner for anything you make off an unofficial product, honestly I don't know, I'd have to ask my lawyer it's a pretty complex area for my minimal understanding of it.
The reason the files are here for free are for the very fact you stated Dazza, they are copyrighted material and selling them would most likely see you with a cease and desist letter down the track, possibly never but I'd prefer not to take that risk. If people want to sell it then what happens after that is their responsibility.