i reread your op and i have to say no were did you post that the seller agreed to refund any money after the purchase. with most used purchases its no return no refund. typically the seller doesnt want it back. its up to the buyer to ensure he is getting what he wants. case in point i just bought some spacers. i was sure 20mm would do the trick and sure enough it didnt. i emailed asking for a return and was told no. i should have made sure it was the right spacer. its on me not the seller.

did he specify it wasnt vin specific? or was he just sellng a tcu and you assumed it would work? not every transaction goes smoothly and for me i have been fortunate that only a couple of low priced items burned me. for myself my reputation on the forums means more to me than any sale. maybe the seller isnt as worried about what folks think. cant say until he decides to post his side if he chooses.