My question involves a consumer law issue in the State of: California
We purchased a truck from my father-in-law approximately 3 years ago and has been sitting in my driveway. We have not registered it and the title is still in my father-in-laws name. It is not drivable. My husband had mentioned that my son-in-law might want to purchase the truck, but when I checked with my daughter. they had said no. Anyway, when one of my friends were over, I was telling him that my son-in-law didn't want to buy truck and he said that he knew someone that may want to buy it. My husband was out of town and was unreachable when all this was going on. The guy came over and gave me $280.00 towards the truck. I wrote out a receipt for the money and also how much more was owed on it. When my husband finally called me, I informed him of what was going on with the truck, but he stated that he did not want to sell it anymore. The only reason he was going to sell it to my son-in-law was because it would be staying in the family. Now the guy that gave me the $280.00 states that he has a binding contract and that he put money down on it and that I have to sell it to him. He tried to give me the rest of the money on several occasions, but I refused to take it. I told him I would give him back his money as soon as I can, but he says that he can sue me in court and I would have to sell him the truck.
What can I do if he refuses to take his $280.00 back? This guy has a vehicle that he drives now, and he doesn't even have a valid drivers license. Could he take me to small claims court and sue me for more money than the $280.00? Do I, as a seller, have a right not to sell the vehicle?

