You can use models that you were granted the appropriate rights to use, via the licensing agreement you entered into during the purchase or acquisition of the model.
Beyond that there is no way to say, in general: you must review (or you must task a lawyer with reviewing) each model and how you use it in your game, and compare that to the license for that model. For example, it's possible you were granted a license that allows you to render out the model and use it for marketing purposes but not to actually distribute the model geometry or render it in real-time. It's possible you were granted the ability to use the model however, as long as you don't charge for the product you're selling. You may need to make certain disclaimers about where you got the model. Et cetera, et cetera, et cetera. The list of possible entanglements and requirements is too long to enumerate here.
If you do not have or cannot find a license for a model it's probably safe to assume you cannot use it.