title: Shopping Cart reserve product
body: <p>Following on from this question <a href="https://stackoverflow.com/questions/1357143/shopping-cart-and-stock-management">here</a>, how does one reserve a product in a shopping cart when a user goes to pay? What if the user abandons the purchase and does not come back to your site, how will you unreserve the product if the page is not being reloaded.  For that matter how would you reserve the product in the first place? I am creating a cart using php mysql and using paypal web payments standard. 
  Thanks</p>