The former owner of a stamping and scrapping store in my town holds a "rubber rummage sale" twice a year. She used to hold it at her store; now it's held in the community center at a mobile home park. I think she said over 30 people are planning to participate. Merchandise is not limited to rubber stamps, although there are usually several tables of nothing but stamps.
Sellers are assigned a number in advance. Any item they want to sell needs to be in a plastic baggie (or other clear packaging), with an index card that has the seller's number and the price on it. If the item is a stamp, she asks that you stamp the image on the index card so that people can see what it is.
When something is sold, the cashier keeps the index card. After the sale is over, she sorts the cards by the seller number and tallies each seller's cards. I think she keeps 10% of the proceeds to pay for her time organizing the sale and to pay for advertising (and I suppose the room rental now that she no longer has a store).
At some point after the sale, the sellers come back to get their money and any of their items that did not sell. They also get back their cards for the items that did sell.
Grand Goddess of GPS of America - BCBW Chapter