I'm Lucy, and I'd be happy to answer your questions today.
Massachusetts has what's called a "lemon aid" law to protect buyers of used cars. If the car doesn't pass inspection within seven (7) days of the purchase and the cost of getting the repairs to make it pass will cost more than 10% of the purchase price, then you actually have a right to cancel the sale. It doesn't matter if you bought the car from a dealer or a private party, and if you bought the car from a private party, he's bound by the law even if he didn't know about it.
Then, within 14 days after you make the sale, you must send the seller a written statement that the car failed the inspection, plus a written estimate for the cost of repairs, and a note that you plan to void the sale under G. L. c. 90, Section 7N. Make sure to keep copies of everything you send him. The letter should be sent via certified mail with a return receipt so you can prove you sent it. You also must deliver the car back to the seller, preferably with a third party witness. Any adult friend or relative can act as a witness - you just want someone who can testify if necessary that you returned the car. That statute also allows you and the seller to agree in writing that he will have the repairs made at his expense rather than take the car back and give you a refund.
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