Is the previous owner acting like he is going to refund your money ? Have you asked him point blank to take the car back and have him refund you the purchase price plus $750 plus gas and time... To get this to happen you have to very casually put the fear of god in him by saying that if he will not refund everything and make this right you now and only now have no choice but to pursue him legally - you do not have to clarify what this means, only that you have spoken with your family lawyer who says he is ready to take care of this if you ask him to... the PO should balk at this point and offer to make things right.. if he doesn't then go after him, you know he lied to you!! Make it your life long mission to resolve this in your favor and don't back down. But first you have to sound very calm, and try to act as if you have resigned yourself to let your family lawyer have it and you are calling him one last time to give him one last chance to make things right... forget the mechanic if you can and get a refund and go forward or fix the car and get over it... I could never ever get over it though ..
Dont back down if you dont want to!!! You know he lied to you!!