While one's (such as, a street seller or a
stranger) back is turned to you, you walk away
quickly, so when one's back is turned back around to return to you, they'll see that
you're not there anymore.
A product seller at
the Flamingo Hotel and Casino had given me a free iPhone 7/8 Screen Protector, he then was trying to sell me an iPhone Screen Protector for my iPhone X phone. He had turned his back to me to walk over to retrieve the
appropriate screen protector, which gave me the
opportunity to ghost him.