Write the seller back....

Here's the exact language on E-bay..

Credit Card Surcharges
An eBay seller may not charge a fee, often called a "credit card surcharge," when accepting credit card payments. This surcharge, which is an added cost to the buyer over and above the final sale price and shipping/handling, is not allowed under the laws of many states, including California. For more information, see:

http://www-s2.visa.com/fb/merch/biz/govt/surcharge.html
http://www.mastercard.com/consumer/cust_serv.html

Please be sure to check our Prohibited, Questionable & Infringing Items pages.