PayPal does provide what is called "Guest Checkout" where buyers can use a credit card without creating an account or logging in. Depending on how your payments are integrated there are different ways to get this working best so that the Guest Checkout option is prominently displayed.
The smart buttons include nice credit card icons, and when you click on a CC icon it gives a buyer experience that is expected for credit card payment without requiring a login. That's what I would recommend.
Angell EYE - www.angelleye.com PayPal Partner and Certified Developer - Kudos are Greatly Appreciated!