Lol,
"i wanna buy it, but i will not pay fair price"
to be fair, the fair/market price isn't retail/full price, its about 30 to 80 cents lower for a key. why would I pay a stranger full price when I know I won't get scammed buying them from valve?
but you are also dealing with bitcoins, where a value of 15$ per btc can crash to 11$ in 24 hrs.
therefore i think the 1:1 price would be fair to account for risk for the seller