As a friend, I don't understand why he'd even think it was your fault anyway. How would he deal with it had you bought it on his behalf from somewhere like eBay? Would ha have demanded a refund from you or even the seller because of this?
How old is your "mate"? If he's able to install a graphics card, surely he's old enough to understand how private secondhand sales work?
How old is your "mate"? If he's able to install a graphics card, surely he's old enough to understand how private secondhand sales work?