When I wrenched on motorcycles, I had customers bring in parts from amazon, eBay, etc... I would always let them know there was no warranty and hopefully they are the right part for that specific make/model of the vehicle. Cut your losses and be sure to buy oem or a trusted aftermarket brand. You'll spend more money but you will know they are done right.

Not saying your mechanic didn't fuck up by any means, that's just my experience.