I have been preparing to start an auction on the Avon with Britny Facebook page. The way I would do this is to post pictures of specific items. Then I would start the bidding at a low number. What people would then do is comment under the picture a new bid raising in increments of .25 or .50 depending on the item. The person with the highest bid by the end date will be able to purchase the item at that price. Here is an example:
Bid Starting at $1.00
Increments of .25
You would then comment on it with 1.25. Then someone else would comment 1.50 and so on until a final price is reached.