Used cars in Zihua and/or Mexico

We are curious as to how and where to purchase a good used vehicle in Mexico and in particular Zihuatanejo. I have noticed the odd location where cars are lined up with $$$ signs in the windows and there is usually someone around. And of course there are those that are still being driven with $$$ and phone numbers in the back window.

I have not noticed any used vehicles at any of the car dealers in town but then maybe I'm just not looking in the right place.

I am wondering if we should be looking in town or should we go to a larger centre (Morelia?) or should we just consider buying a new one from a dealer instead?

Thanks for any and all information. And no this is not, at least right now, a call for offers to sell me your car but thanks anyway!