I agree. There are some new optional rules for allowing a successful Diplomacy check to modify the price of purchased items by -10% (can't recall what the DC is though). I think a similar rule should be allowed to increase the asking price of an item being sold by +10%. In fact I find the 50% rule to be a bit oversimplistic. It doesn't take into account reputation, negotiating skill or connections. What I mean is, a successful gather information check could help a PC find an interested buyer for his item. Knowledge (local) could likewise help in knowing who best to approach with some unusual items. Diplomacy is of course the best skill to represent bartering. I would think that a successful DC 20, DC 30, DC 40 or DC 50 Diplomacy check should allow a PC to cut a better deal than a measly 50%. Still trying to figure out the best mechanic though.