When planning a conversion rate improvement project, it's a great idea to start with tweaking your checkout process.
But where in the checkout process do you start? Many are tempted to begin by shortening the number of steps in the checkout process. While this has improved conversion for many sites and is a good idea to test, it shouldn't be the first thing you optimize.
More important is getting the customer into the checkout process to begin with. Typically, there is a gate between "Proceed to Checkout" and Shipping/Billing information in the form of a login/guest checkout screen. This is most likely presented in 1 of 5 formats:
1. Login screen (no guest checkout option)
2. Login screen with guest checkout option
3. Login screen with guest checkout plus account creation option
4. Default to guest checkout flow, with option to sign into account
5. "The Amazon" (single email field with radio buttons for password)
The problem with all of the above except for the Amazon approach is customers must decide between input sections. This requires the customer to read and make a choice. Sadly, you can never count on everyone to read instructions, meaning you will always have a segment of customers who will trip over login screens like this. Here's an example from Jakob Nielsen's usability blog:
In our study, a person who was already a registered user on Kayak had great trouble logging into the site on this screen:
How can that be? The distinction between "sign up" and "sign in" is clearly marked! Sure, if you read the blah-blah. But users don't. Their eyes and mouse go straight to the field where they can type.
That's what people want to do: they want to get things done. They don't want to read.
The golden rule of usability is "don't make me think," and the more options you give the more you make the user think. Using Amazon's approach, Sears streamlines its login screen, with even less instructions text to read than Amazon:
Only when the user selects "No" does the text "You will have a chance to register after checking out" appear, saving existing account holders from extra reading and thinking.
A second runner-up in the simplicity category is the default guest checkout (skips the login in screen) with optional account login box. We tested this approach against our original 3 option process with the Vancouver 2010 Olympic Store and achieved a 21.8% lift in checkout completion.
I challenge you to test your existing login screen against "the Amazon" and the default guest checkout first, then look at other points of friction (like presence of a progress indicator) to further improve results after you've determined the best login approach for your site.