Car dealerships screwing people!?

my dad was going to buy a vehicle from teh car company and he got tricked into buying two vehicles and they told him the deal was not final that he had to come back today and he had his dad co-sign for it and they put the truck in his dads name instead of my dads. he went to change his mind today about buying the vehicles after talking to my mom and realizing how stupid he was and they are now not letting him go back on that deal. idk if you'd know anything about this but is there a way he can go back on it? they fed him a big line of crap and tricked him into buying a f250 and a mini coup. so when he went to take the vehicle back today they told him if he left it on the lot thats considered repossession and they will file it against him. are they aloud to do that???