In a quantity buy (5 or more) The price would be lower. It really depends on what it is that they are selling. Really clean old desirable ones? A mix match? When asked this question I have always said put them on consignment at a good LGS. You might pay 20% of the sale price, but you will get what the market will bare. Auctions are a better deal, for the seller, but they have their costs as well.
