Many ecommerce websites will send you an email with a coupon code if you start to make a purchase and then do not complete the purchase. If you want to save some money, try abandoning your shopping cart without checking out. Wait a day and see if you get an email with a discount.
The website will need to have your email in order for this to work. So you'll need to be logged in, or have entered your email address. Not all websites do this, but a growing number are.