WHY Do People...

I sell stuff on eBay for walking-around money.  I sold three things in the last couple of weeks, worth around $400 total.  NONE of those winning bidders has paid.

• You bid on an auction and click a dialog agreeing that this is a commitment to pay
• You get an e-mail telling you you have won
• You even got an invoice from the seller
• And you don't pay?  

WTHPPL?