The Quantity is how many identical items/lots are being sold. Most auctions have a Quantity of only one; if an auction has a quantity of more than one, it becomes a Dutch Auction. The Quantity determines how many winning bids will be accepted. If every item/lot in the auction is NOT completely identical (with only slight variances in the quality, etc.) then you MUST create separate auctions for each different item. For example, if you have 2 copies of Comic Book A and 3 copies of Comic Book B you cannot create one auction for 5 items, you must create two separate auctions - one for Comic Book A with a Quantity of 2 and one for Comic Book B with a Quantity of 3.
Example: if an auction has a Quantity of 5, and more than 5 people bid on the auction, only the top five bids are considered "winning" and are legally bound to pay for the auction.
If the Quantity has already been met, bidders may still continue to place bids to compete for the winning slots. See the FAQ on Dutch Auctions to read more about how competing bids work with a Quantity higher than one.
If you are posting an auction with unlimited quantity, we suggest you set the Quantity to "99" to avoid confusion and to make sure all winning bids receive the notification email at the end of the auction.