As a Seller you can cancel your Ask at any point up until it's matched with a Bid, at which point you are committed to selling the item. Once a Buyer has agreed to your price, it's expected that you will commit to the sale, so only list Asks that are ready to be sold.

StockX functions at its best when every Ask on the site is real, live and dependable. This fosters Buyer trust in StockX and helps Sellers like you sell more! In short, this means that you get to spend more time as a Seller on StockX actually selling your items.