The watch list is there for buyers to put items they are interested in until they decide whethere to buy or not.  Once they press the buy button, they are committed and they have removed your item from sale so no one else can purcahse it.  Even B+M stores don't hold an item while you decide whether you want to pay for it or not.

Actually a lot of B&M stores hold items for up to 7 days without any deposit.