I don't think you really need get into a law suit to get back your deposit.
Most of the cases, the dealers give back the deposit no matter how the agreement was drafted, assuming that you haven't driven the car home.
1. Talk to theri senior managers (or the president) about the issue. Normally the sales guy doesn't want to give back your deposit, because that will affect his commission. If you don't feel comfortable talking to them, you can write to them. Politely and assertively.
2. Or get an experienced person to deal with them.
3. The last option is to get a lawyer to draft a letter for you. Businesses are relunctant to get involved in a law suit for only a couple of hundred dollar's profit. It is much more expensive for them to deal with a potential law suit.
Stay cool and don't feel frustrated. You have a very good chance to get your money back.