BBB....then small claims court for the damage done to the vehicle while in thier custody. On top of it a cleaning bill and a bill for the repairs that were made fixing that mechanics/car lot owner made that were sub par. Then on top hit them for lost wages and aggrevation. And yes I would say something about the money involved i.e. "thier need to compensate you for the above" if that doesnt work make sure you have all your ducks in a row....paper work, warranty, any conversations and if there were witnesses. then I would even take out an ad saying
"If you have ever had warranty or repair issues by _________ garage please contact _______________. ". The reason for this research is most times people don't know they are dealing with a lending predator that does not stand behind what they sell or warant, this is just hear say but can sometimes be use to set the stage in your case, especially if you tell them to please contact the BBB if they have a valid complaint so others can see what type of dealer this guy is. Your job is now to do what a lawyer calls discovery to support your claim.

If you want to see the business go from good stealing from the less than fortunate to the lees than fortunate going else where then this is your oportunity
GL