Buyers can only have 100% positive, eBay does not allow anything else so 100% as a buyer means nothing whatsoever

It is also possible it is a hijacked account 

Has the person been 'active' recently , or does their last feedback show as 'over a year ago'

There have been three cases at least of hacked/hijacked accounts in the past two weeks posted on the forum here, so before you do another thing, please, triple check. Better safe than sorry