Not Reading the Contract
It is not possible to overemphasize the importance of reading and understanding the entire sales contract, including the fine print on the back. If you don’t understand something, ask for a copy of the contract, then have it reviewed by someone you trust before you sign. Do not accept an explanation provided by a dealership employee.
Also, recognize that the salesperson’s signature may not bind the dealership to that wonderful deal you have just negotiated. At some dealerships, the deal is only binding after a manager or dealership principal signs the contract. The fine print should clarify these details. Finally, be sure to take a copy of the signed contract with you even if the transaction will not be completed until later.