You've paid your own lawyer for advice. You received it. Take that advice!
I agree with your lawyer. Depending on what they wrote on the IOU - you may be able to get a safety check on the car. If they wrote "I owe you a (type of car) in good working condition" then you have the right to see if they complied with their part of the contract - did they give you that type of car in a good working condition?
No matter what, keep the IOU they wrote to you.
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