I don't think this happens very often. The terms and conditions of the purchase agreement (order) may say what happens in the event of a cancellation. If silent on the matter, the 'buyer' would likely be in breach of contract and liable for the dealer's losses which may be covered by the deposit.

This situation must have occurred many times in respect of car purchase and there may be common law which would prevail. I'm sure there will be clarification on this from the lawyers on here.