I have much the same views that is, the model you're trying to sell is most likely available for free elsewhere.
There are a couple of other places I've seen that sell models.
http://3dmodelworks.com/ being one of them
http://turbosquid.com is another i'm sure you've heard of.
There was that other one that was advertised on cgtalk that was specifically for cars that seemed to do alright.
I haven't sold any myself, but I don't see anything wrong with selling them. If a company requires them at really short notice then I see no better way than using someone elses.
You should have no problems selling your models mate. People at most of these places are selling crap arsed models, and getting paid nicely for them.
I remember when I was working at the crystal company, we went looking for models... All the ones that we found were too crap, low poly, or just even more crap. So I had to make them myself. Which cost the company more to pay me then it would to buy the models. So in that respect, the more the high quality models that are available, the better it would be.