Waxman,
I have a regular retail used car sales lot at my detail location, so for me I have all the proper licenses, zoning, etc.
As far as trying to sell someone else’s car as a consignment, you should look into the local ordinances first.
Second, selling or "trying" to help someone sell a car that you do not own as a private individual would be considered curb stoning in the auto industry. Depending on what state and city you are located in, you may or may not be able to even sell a vehicle that you own at your commercial location. Most local towns, boroughs, and townships look the other way. If it is your own personal vehicle so what. Most used car dealers, however, do not look the other way if the vehicle is being displayed advertised, etc for sale at your location. It all depends on who really cares and who doesn't.
The reason curb stoning is illegal, are the vast amount of regulations there are in the auto industry, on the local, state, and especially the federal level. It is getting to the point used car and even new car dealerships are under a very powerful microscope with the collapse of the financial markets. Someone who does not have the proper licenses (there are many) to even have a dealership let alone sell a vehicle can do what they please to the general public when it comes to selling a vehicle. This alone has put a very dark cloud over the auto industry for years. Most people do not like having to deal with auto sales, even if they have to when they need a new car or truck.
Mike