Firsty the box would have had to sustained pretty bad damage for that which he should be able to prove.
Secondly i think that the bottom of the metal plate has been bent from him fitting it into his case/motherboard, we have all had those case's where you really have to wiggle and put a lot of pressure on the card to fit it, Also he may have damaged the fan the same way, He may have hold of the card in a way that an excessive amount of pressure is being put onto the fan whilst forcing the card into place.
As i said, the box is key to this, Did he send you a picture of the box? if i recieved a graphics card in which the box had sustained the amount of damage to bend the metal and put heavy enough pressure on the fan to stop it working i would not except it?