It always makes sense to look for payments through credit cards instead of cash or through checks. Asking for payments through credit cards is a smart way to find out more about the credit worthiness of the client. If he/she has a damaged credit standing then it is unlikely that they will be able to pay through credit cards.
Finally the documentation aspect of the luxury car must be fully taken care of. For example the registration certificate, fitness/roadworthiness certificate and other such documents must be up to date and fully valid. In the condition of the car, internal and external must always be of the best quality.