Just my opinion but give em a chance to make it right before you go bad mouthing anyone .If someone repeatedly ignores your requests or is unreasonable then call them out publicly. My .02C
x2 give him ample time to respond, some people travel or otherwise can be away from their computer for days. This brings to mind a similar situation all got sorted out in due time.
If the part is not usable he should take it back and refund your money...chances are he will do just that...most people on FABO are reasonable...not worth losing his reputation over a relatively small-dollar item.
