Why doesn't Paypal Guest Checkout show?

When paying through a checkout page on PayPal.com, there is sometimes the option to pay by credit card without logging in to PayPal. This is known as "guest" checkout mode. 

To enable guest checkout on PayPal:

1. Sign in to your PayPal account

2. Click the Profile icon at the top right.

4. Click Profile and settings.

5. Click My Selling Tools or My Selling Preferences under My Profile on the left.

6. Click Update next to Website Preferences.

7. Select On under PayPal Account Optional.

8. Click Save.

This will enable Guest checkout on your PayPal account. However, guest checkout may not always be available to your customers based on a number of factors;

Fraud prevention PayPal has fraud prevention measures in effect for all transactions and therefore, in some cases, PayPal might prevent a customer from using the guest checkout if they feel that the transaction poses a certain risk.

Incorrect email address Your customer entered an incorrect email address or an email address that PayPal was unable to verify.

Location is not supported The ability to allow customers to pay via PayPal through guest checkout is determined by your local PayPal organization's security and risk management policies.

PayPal has been "split testing" their checkout with and without guest checkout enabled. Because of this, PayPal can't guarantee whether guest checkout will always appear. 

This is the message and reasoning on this from PayPal:

"For customers that don't want to create a PayPal account, but instead pay with their debit / credit card (account optional) some will be shown this payment option, but others may not be shown it. This is due to changes in the checkout experience we implemented when introducing our new checkout experience.
In this new checkout flow there is no guaranteed way to display the guest checkout first or by default. In some cases the option will not be shown at all.

In some instances, the buyer will be able to pay with a debit/credit card directly and in some others they will only be able to open an account using a debit/credit card.

This can depend on many factors like cookies, mobile/web, time of the day, and many other variables which makes it impossible to predict.

We also found, in intensive A / B tests that...

- drop-off rate is 20% higher when merchants show the guest checkout by default

- 27% increase in total customer (post PayPal integration)

- 15% increase in total customer spend (post PayPal integration)

- 1.8 x more transaction per customer (PayPal vs Total Customers)

- 2 x more spend per customer (PayPal vs Total Customers)

[Nielsen Online Buyer Insights, 52 weeks pre-/post-PayPal integration. Study completed November 2013]"