It would only be against ebay policy for them to buy from you with another id if you had added them to your blocked bidder list after the first transaction. If you did do that then contact ebay again using the call me back option and explain what has happened again, Keep it factual, no name calling or personal attacks against the buyer. If that doesn't work call back a few hours later, eventually you may get somebody to listen.

The buyer protection for pick up items with Paypal is far more rerstrictive than for a posted item, if you ask for and make a copy of photo id when they come to pick up you should be OK as you have all you need to contact the police if they try to diddle you.