Alright, that sounds nice. But has anyone ever rented your hash power?
I don't see the reason why anyone would want to rent, they would have to pay more including the markup than what they would earn.
My hash power is rented 50-70% of the time (for around 10-20% more than solo mining would pay).
There a few different reasons to rent hash power, most are nefarious, and the two big ones are to wash money or hop proportional pools (although pool hopping isn't possible for those renting from GPUMax). Somebody is profiting off your GPU in some way or another.
Some people do use it as an easy to to buy Bitcoins (Ie, rent GPU's via PayPal and use them to mine), but AFAIK GPUMax only allows people to rent using Bitcoins, so that one doesn't apply to GPUMax either.
Another legitimate reason is to use your GPU to merge mine, so they actually get the Bitcoin's mined + other crypto-currenices mined. This is usually only 1-2% more profitable though, not near enough the rates GPUMax renters are paying.