Ask a Lawyer and Get Answers to Your Legal Questions
Start by getting a copy of the contract that you did sign. See what the contract says.
If the contract is in fact a non-refundable deposit, you are not going to be able to force the dealer to return the money (although you can try getting them to do so in order to improve their customer image, etc. - you can even try a BBB complaint).
But if the contract does not have a "non-refundable" clause in it - the vendor cannot try to interpret it as one later, or insert one after the fact, and you are entitled to a full return of your deposit.