“Reselling basketball sneakers has become a cultlike atmosphere,” said Marshal Cohen, chief industry analyst of the NPD Group. “No one is watching over all this money changing hands. So it seems like it’s being done underground, but it’s perfectly legal. And it’s exciting to them because it’s a real form of income.”

Teenagers know what draws top dollar and are careful to walk like ducks so as not to crease new shoes they plan to sell quickly. (The collectors look for their sizes to wear the shoes, and men’s sizes are more valuable.) At these events, experts check the soles, tongues and other marks to authenticate shoes. At the convention at the Hotel Pennsylvania, cleaning stations were also available.

While money or shoes change hands successfully on these Saturday afternoons, trades using Instagram and other social media have become so popular that a new shoe — ordered online with the purchase snapped via Instagram — may not have even arrived before it is resold by some enterprising youth. Online and off, business is brisk.

“I can see sneakers becoming even bigger than the baseball card scene,” predicted George Rahor, who teams with his son, Steven, 14, in “Street Heat Sole & Style Expo” events, and who used to run baseball card shows in the 1990s.

Just like the aura around other highly prized collector’s items, sometimes it’s the deal that doesn’t get made that generates the most buzz.

At the Manhattan event last month, one young vendor turned away $98,000 in cash for his Nike Air Yeezy 2 “Red October” sneakers, designed by Kanye West and signed by the artist himself onstage at the Nassau Coliseum in February.

“I know I could buy a house with this kind of money,” said the vendor, Jonathan Rodriguez, 18, of Deer Park, N.Y., who said he planned to enlist in the Air Force. “But I’m a huge Kanye West fan. I can just work to get the money. The only way I’m selling them is if there is a reason that I need to sell or I’m offered life-changing money.”