He was running the card 100% load 24/7, how does that warrant an RMA? No card that it used for bitcoin mining should be entitled for a "free" replacement. How many lies will you tell them to get a new free card?
That would be entitled to an RMA. Pushing it past 100% (overclocking/overvolting) breaks the terms of the warranty. Using it right up to the terms 100% does not.
Overclocking doesn't with GPUs, overvolting DOES.
Again, why do you think overclocking is readily available in Catalyst, with no warnings about warranty?