This article is from the eBay FAQ, by William B. Shaw firstname.lastname@example.org with numerous contributions by others.
If they state in their auction listing that they do accept that form of
payment, insist upon it. You have every right to expect the seller to live
up to the terms they stated in the auction. If you get a neg, handle it
If the seller didn't state in their auction listing that a specific form of
payment is acceptable, you should have clarified that bit of information
before you bid. Note that many sellers will check the Visa/MC option for
payments by eBay Payments and PayPal. EBay considers this acceptable. If you
try to force a payment type onto a seller, be prepared for a no sale and
possible negative feedback.