I've seen a number of recommendations to support guest checkouts. eg Should registration be optional on an e-commerce site?
In an e-commerce site where logged-in customers can view previous orders, delivery address, etc, what's the appropriate thing to do when a customer registers with an email that's already been used for a guest checkout?
- Forget the guest order and treat the registering customer as a completely new customer, because that better respects the customer's privacy; or
- Associate the previous order(s) and address(es) with the new account, because it saves the customer time;
Similarly, what about a customer trying to do guest checkout with an email that's already associated with an account? Ignore the existing account or alert the customer?