I came across this excellent article on 10 worst things than can happen during the online checkout process. It inspired me to add to the list:
1. An "over-persistent" cookie: If a consumer added something to their cart in the last visit and came back later to buy other items, allow the consumer the option to delete the items without jumping through hoops and don’t be a nag and try to push the item.
2. If an item is available in multiple colors/sizes, offer the option to change color/size of order in the shopping cart itself. Or, at least make it easy to go back and change the order. Like the article says, don’t trap customers in the checkout and force them to open a new tab to go back to the shopping page.
3. Make it easy to identify the “Ship to” address and make the customer confirm the address before confirming the order. This will save both the customer and the vendor hassle, time and money.
4. Offer options for partial payment: the customer may have a gift card or store credit that they want to use, and may only want to pay the balance with a credit card. Many sites offer the option but don’t explain that they do this. If you do something customer-friendly, advertise it!
5. If an item is out of stock, offer to notify the customer when fresh stock arrives. It’s easy to do, costs the vendor very little and is an excellent marketing opportunity to bring a customer back to your site where they might end up ordering other things while they’re there.
6. If you have a brick and mortar store in addition to an online store, emphasize it. This is a great feature to emphasize particularly if returns can be dropped off at the store and don’t have to be mailed back, or if customer can get free shipping if (s)he offers to pick-up in store. In-store pick-ups/returns maximize the opportunity for impulse buys.