If you are beginner forget cars in general. To be able to sell car models here you have to be on a very very high level because competition is very strong. First you have to beat legit competition (legit artists), after that you have to beat thieves, and trust me, no one can beat laser scanned 3d model stolen from a video game which are selling here for 2$. It's just isn't worth the effort and time to fight against that. The only thing you can do is to model cars that aren't availabe to thieves and because of that aren't available on sale here, which is science for itself.