An installment contract is a single contract that is completed by a series of performances–such as payments, performances of a service, or delivery of goods–rather than being performed all at one time.
After Purchasing a Vehicle You need more than a bill of sale to transfer ownership of a vehicle in Pennsylvania. Additional documents will need to be presented to make the transaction official.
A bill of sale is more akin to a receipt rather than a contract. Since it is such a simple document, there is no way to truly enforce it. If the bill of sale is the only document you use in a transaction, it is best to ensure there is enough detail on it to make the transaction enforceable.