You just want a car in your game? Or do you want to script the dealer?
If you just want a car:
https://sampwiki.blast.hk/wiki/AddStaticVehicle
Just add that in your OnFilterscriptInit or OnGameModeInit, and your done. You can get the positions easily with MTA, just search on ******. You can then convert the .map file on the web, straigth to the AddStaticVehicle format