Usually MPB would accept that back since they lied on their part about the condition. Had the same thing happen to me last year. Bought a EFs 24-70 2.8 II in “like new” condition, tested it a bit at home, all was fine. The next day i photographed a wedding, and after 10min of shooting, the camera threw a error code that the contacts of the lens were broken.

That was tough to explain… Nonetheless they apologized and i was able to send it back and get my money back

Absolutely nothing wrong with this, this is how photographers who are still starting approach new customers