If you've customized your login page and are a member focused organization, but want to sell ecommerce merchandise to the public, you can setup a Guest Checkout option by following these steps.
First, you want to program the "Guest Checkout" button to link to /login/guest this will enable the platform to recognize they are a guest and route them through the appropriate process.
Once this is in place, you will need to determine if they are trying to checkout from commerce (or something else). You can do this by viewing the data in the curObj object and look for the value under prev_page. If this starts with '/checkout/shipping' then they are checking out for ecommerce and we will route them to the shipping screen upon registering as a guest (or whichever path they choose).