On the "Shopping Cart" page, you will see a "continue checkout" button and an orange "express checkout" button.
The "continue checkout" button will ask the customer to login, and then select shipping, and then make a payment choice. On that payment-choices page, the customer will see both "PayPal" and "Credit Card" options. The "PayPal" option is Express Checkout, and the "Credit Card" option is Website Payments Pro.
If the customer uses the orange "express checkout" button, they will bypass the login and shipping and payment selections, and never see Website Payments Pro, because they've already selected Express Checkout. If you think your customers aren't smart enough to accept that, then you can turn off that orange shortcut button in your ZC admin Express Checkout settings, which will then cause your shopping-cart page to only show the "continue checkout" button. They will still be able to choose "PayPal" or "Credit Card" on the payment choices page.
Simplest way to understand it is to try it yourself.
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