Originally posted by: dirtboy
Contract law is simple and I've been through a dispute with my last lease and I won. Normally I'd side with your mother. However, contract law says that both parties enter the contract in good faith. Your mom used a discount code that turned out to be illegit. She failed to give them her code and in your own words, guessed. By doing so she attempted to defraud the other party. In the case of fraud, the other party is not legally required to uphold their end, thus making the contract void.
The dealership wouldn't be repeatedly threatening taking your mom to court if they didn't have a case.
In my case, the dealership briefly threatened to have their lawyers call me. I told the sales manager to do that so I could explain basic contract law to them. I won.

However, I made no attempt to defraud them. The dealership made an error on the lease agreement in my favor, then later wanted me to give it up.