I simply read the readme file. Almost all say that it's okay to use in away, commercial or non-commercial.

However, every once in a great while, the modeler says NO. You can't use his items in any commercial way. That clarifies things greatly. I won't. I won't even download it.

However; No credit will be given the modeler because no one will see his work. I DO credit people for their work.

People like Yanelis3D, Carl Culberson are great artists and modelers and give away work they think isn't up to their standards. Work that just blows me away. Or sometimes they just like to give. I always give them credit. If you take the time to contact them, you'll find they are pleasant, gracious, and quite generous.