If you have a PM or Text from buyer saying he refuses insurance, then it shouldnt be your fault.
Work w the UPS to find the wheels and ship them to you or the buyer. If the buyer refuse, request the wheels he recieved back, and refund him 1/2 of the money till you sort it out w UPS. When the other two wheels arrive or are compensated for, refund the buyer.
Take it as a leason and dont sell stuff to people who dont want to pay insurance.