DETROIT: The pair of allegedly rare Air Jordan sneakers arrived last month to the bunker-like Authentication Center of StockX, a Dan Gilbert-backed company that is one of Detroit’s fastest-growing startups.

The black-and-red Jordans were purportedly from 1995. For sneakerheads who collect such things, that’s close to antique.

If these shoes were authentic, they might fetch $500 on StockX’s online marketplace, which functions like a stock market for the re-selling of hard-to-find sneakers, sportswear, watches and handbags.

But this pair didn’t pass the smell test.

One of the center’s “authenticators” took a whiff of the Jordans and immediately knew something was off. Smell is one of the 25 to 30 indicators they can use to distinguish a legit shoe from a cheap knockoff.

“It just had a very distinct smell that we hadn’t smelled before,” recalled sneaker authenticator Sadelle Moore, 31, of Detroit, “so we knew automatically that was fake.”

This army of dozens of merchandise authenticators form the backbone of StockX and its effort to become the world’s leading resale marketplace for scarce consumer goods.

Launched in February 2016 with just a handful of employees, StockX has grown to 370 employees, including about 40 workers at its western U.S. authentication center in Tempe, Ariz.

The company says it processes thousands of pairs of shoes a day and handles about $2 million in daily sale transactions. It plans to open new centers in New Jersey and London this year.

StockX CEO Josh Luber, 40, said one of the company’s latest challenges in finding enough people to hire.

“There are 200 people we’d hire tomorrow, if we can find the right people,” Luber said. “We’d triple the engineering team, we’d double the authentication team, we’d double the customer service team. That is just part of hyper-growth.”

StockX is headquartered on the same floor as Gilbert’s personal office in downtown Detroit’s One Campus Martius building. Gilbert founded mortgage giant Quicken Loans and owns the Cleveland Cavaliers.

Roughly 70 percent of StockX’s merchandise is currently sneakers, followed by about 20 percent streetwear and about 5 percent watches and handbags. StockX only sells authentic sneakers that are unworn and in their original box.

The company says it overtook eBay last year for sneaker resales. Its competitors also include online sellers and platforms such as GOAT, Grailed, Flight Club and Stadium Goods.

There is significant money in reselling sneakers. Shoe companies intentionally produce limited quantities of desirable models, such as the latest Adidas Yeezy or Air Jordans, which makes it hard for consumers to buy a pair before inventories sell out.

Similar to what Kelley Blue Book is for used cars, StockX has already become a leading gauge of market value in the sneaker resale world — even for transactions that don’t happen on the StockX platform.

Weeding out replica sneakers from authentic originals is key to StockX’s business model. The company guarantees that the merchandise it ships is “100 percent authentic.” So if too many knockoffs were to get through and customers then complained on social media, StockX’s brand would suffer.

Luber said there are strong incentives to make knockoffs of rare sneakers and pass them off as genuine.

“It’s a really big business because of the margins that these fake factories can make,” he said. “They can make a fake shoe for $40 in China and sell it for $1,000 on eBay.”

Ebay does not authenticate resold sneakers.

StockX bans sellers from its platform that willfully or repeatedly attempt to sell fakes. Would-be buyers whose orders are stopped by the discovery of a fake get refunds if no similar item is available.

Those who alleged to have received fakes said that after they notified StockX, the company gave them a full refund and a $20 discount code for future purchases.

StockX sneakers authenticators go through a 90-day training period. They study a company “fake book” showing telltale signs of knockoffs. They also examine actual fake sneakers that StockX encountered in the past.

“We bring in fake sneakers, we rip them apart, we note every single difference between all of them. And then we teach people, ‘Here are the real ones, here are the fake,’ ” Luber said. “It could be different color stitching, it could be different materials, it could be different packaging. Sometimes it’s the box.”