Some people ask for permission to redistribute models made by others. They may not give credit on the web page but they do in the read me file. Other people blatantly steal them and say they are theirs. If a model was purchased they may have a right to use it commercially, but I doubt if the bought the entire rights to the model so they could freely redistribute it ( legally ). Depending on what country they live in they could be sued for copyright infraction. People think that nobody will know or see that they are doing any wrong. But most people in the CG community will contact the creator, when they see this sort of thing going on, ( that goes for image stealing to ). I say if you know for sure someone is laying clam to someone else's work ( of any type ) to contact the creator and let them know. They will know if they gave permission or not.

Stephen Ray