Beware of contracts presented by the repair shop. If you are presented with a contract by the repair shop when you bring your car in for work, read it before you sign. If parts of the contract make you uncomfortable, discuss it with the repairperson and make changes by crossing out particular clauses. Make sure you limit what you are authorizing the repair company to do by writing the limitations on the contract.
For example, you may want to write on the contract, "I do not authorize work on my car exceeding the total cost of $100." If the time element is important to you, make sure the completion date and time is written on the contract. You may also have to specifically request that the old parts be returned to you.
If you are going to have extensive work done on a car (such as reupholstering your 1965 Porsche), it is best to arrange a meeting to discuss fully with the repairperson the work that is to be done. Take notes and afterward draft a contract that contains the terms discussed. This approach clarifies the agreement for both parties and often clears up potential disputes. After both parties have signed, make copies for everyone and keep the original in your file.