I've been doing a fair amount of bidding in Great Collections recently. Concentrating on Matron Head large cents, generally in VF but occasionally an XF, but never below VF. I figure out how much I'd like to pay for a coin. Then I subtract 20% to cover fees and S&H. The past two times I've bid on 4 coins but have only won one in each case. That's alright. It keeps me from burning through my money too fast. Won one coin tonight; pictures when it arrives.
