I used to have an Ebay account in Italy, which I used only once or twice to buy something. One day I logged in and saw that my name had been changed and that I had stuff for sale that I'd never seen before. I reported this fraudulent use of my account and they asked me to fax them a photocopy of my Italian ID card, my last bank statement and my last credit card statement. Everything that somebody would need for an identity theft. Given that their security is so lax, I didn't want this stuff floating around their offices and refused to fax them anything.
So they blocked both my Ebay and my Paypal accounts. Now I can't buy anything on any site that uses Checkout by Paypal, even if I say I don't want to use my Paypal account to pay. They recognize the email addresses (all of them) and refuse to let me use a credit card for payment. I can't email them, nor even use their forum, without logging into Paypal, which of course I can't do.
To merchants: Don't use Checkout by Paypal! They say they'll let your customers pay by credit card, but they won't if they used to have a Paypal account!