Thrillist points to Dunkxchange that takes place in New York this weekend. Basically, people turn up with their old Dunks and sell/swap/steal them. Thrillist says:
Hundreds are expected to show up, examine prospective deals like old women shopping for cabbage, then walk away confident they haven't bought "fake shoes". As the event's name suggests, the dominant brand'll be Nikes: Dunks and SV's (highs and lows), AF-1's, and Air Jordans…. Prices range from $70 to three thousandish.