When you have a paypal account, one of the terms they have requires you to accept any type of payment a buyer makes. So if the buyer uses a c.c. to pay and you haven't upgraded the account to accept credit card payments, you are required (by the terms you agreed to when you opened the account) to upgrade.
(I don't know if it's automatic now that all accounts take credit cards and all accounts have fees for accepting money; my Paypal account is close to 20 years old and at the time, not all transactions had fees. If a buyer paid with a Paypal balance or a bank transfer/echeck, there was no fee.)
By "sanction," I mean that it's a violation of Paypal's policy to refuse to accept certain types of payments. If they think you do it too often, they can close your account or warn you that they will close it if you don't abide by the terms.
https://www.ebay.com/help/selling/listings/choosing-get-paid/getting-paid-paypal?id=4183
From Paypal:
"Remember, if you offer PayPal as a payment option on eBay (either using logos or text in the item description) you must accept all forms of PayPal payment including payments from an existing PayPal account balance, bank account transfers, and credit card payments. You can't tell buyers that you'll only accept specific forms of PayPal payment. See our Accepted payments policy for more information. When a buyer sends you a payment through PayPal, the money is usually available in your PayPal account right away. However, in some cases, the payment might be "pending" for a few days, or it might be held by PayPal for up to 21 days."