If you purchase something in bitcoin, there's a 2-4% fee tacked on as well. Try to buy something in bitcoin at tigerdirect for instance. Look at the fiat price and then compare it to their BTC price, converted to fiat.
Yes because a miniscule fraction of their customers pay with BTC, I refund most of the difference to my customers via store credit.
http://www.gyft.com does it via points.