lol. You can "turn off" ebay checkout but it doesn't make a difference except on ebay Australia site. Whenever PayPal is accepted as a payment method it is automatically turned on and on ebay and uk you must accept paypal so it is always on by default no matter what.
I'm not 100% sure on the merchant account because I don't have one set up with ebay, but just buy an item of yours and find out. Also, I assume on the eBay invoice with the merchant account that it states in the invoice the buyer accepts visa and credit cards through his merchant account but that is speculation.