I've found that, on average, buy it now asking prices are generally double what a game is really worth. I can't tell you how many times I've looked at completed listings to find an average selling price, only to see new listings asking double (or more). "Hmm, the last 10 copies of this game sold for $25 each. I'll list mine for $50".
Just the nature of the beast. Be patient and you'll find some reasonable deals. You just have to look through a lot of crap to get there.