When creating PayPal "donate" or "buy now" buttons, or integrating PayPal Website Payment Standard with third-party shopping carts like ZenCart, the user will be directed to a PayPal-hosted page where user enters payment information in the form of credit card or PayPal account.
This PayPal hosted page actually will look different depending if the computer that the user is on has used PayPal before or not.
If Paypal believes that PayPal had been used on the computer before, the PayPal hosted page will have the PayPal login box will be the major focus on the page encouraging user to use their PayPal account for payment. Because of the layout of this PayPal hosted page, many user may incorrectly think that they need a PayPal account in order to make the payment. However, that that is not the case. Because there will be a tiny "continue" link where the user can click to use their credit card instead.
On the other hand, if PayPal does not have any evidence that PayPal had ever been used on that computer before, then the PayPal-hosted page will have a split layout where the left side has credit card information entry form for those wanting to pay by credit card. And the right side will have the usual PayPal login box for those wanting to pay by Paypal.
This layout is definately more friendly to those who wants to use a credit card without needing to create a PayPal account
PayPal makes the determination via browser cookies as to whether it thinks the user's computer had used PayPal before or not. Everytime PayPal is used on a computer, PayPal sets a browser cookie on the user machine indicating that PayPal had been used. So the next time the user of the same machine uses the same browser to visit a PayPal hosted page, PayPal will be able to see that cookie and know that the user had been to PayPal before.
You can delete your browser's cookies and then PayPal will not be able to track this and you will be presented with the PayPal payment page that is designed for non-PayPal users.
