They could have gotten your Ebay info from you.
NEVER answer an email from Ebay FROM YOUR EMAIL! Always go to your 'my ebay' page and do it there.
Scammers will often send you something you need to reply to and when you click reply it will send you to a page that looks like your Ebay signin - you sign in and it gets your info that you just typed in.
When I get one now I type in
Username: NICE TRY
Password: Sucka
The best idea is to delete it and never reply whatsoever. I was told this by a computer repair nerd after he had to fix my pc. He says that anytime you follow a link off of an email (even to put in a fake name and password) that you can pick up a trojan virus that has a keystroke logger on it. Nutshell, they get your information anyway by logging password and personal information from whatever you do from there on out on your pc.