How does a buyer Buy it Now without paying?

[collectedbyclyde]

I just had a buyer with zero feedback "buy" one of my items.  However, he didn't pay for it.  How does that work?  How can I protect myself from this? 

This is the second time its happened, and the last time it happened, after 2 days and in response to my last email before I filed with ebay, he requested to cancel the item.  

I get a limited number of items to post without fees, but what if I paid a fee to post this item?  Could buyers troll sellers this way??