I've collected and sold Nike sneakers for 20 years. Spotting fakes is harder than ever, but here's what I look for.

• Shu Cheng has been collecting and selling high-end sneakers for over 20 years.
• He opened Queens' first sneaker consignment shop in 2011, where he deals with fakes regularly.
• Fakes are harder to spot now than ever, but some things he looks for are color, shape, and smell.

This as-told-to essay is based on a conversation with Shu Cheng, co-founder of New York City's sneaker consignment store .IMAGE. It has been edited for length and clarity.

I've loved sneakers since I was in elementary school. In fifth grade, I begged my mom to get me these Air Jordan 13 "He Got Game" sneakers, but they were $100. She got me Filas instead.

Years later, I saved up and bought the shoes myself. My two best friends and I would go around NYC collecting and selling sneakers. Then, in 2011, we opened Queens' first sneaker consignment shop, .IMAGE.

Sometimes, when my mom mentions those Air Jordan 13s, I joke and say, "Listen, you didn't want to buy me those shoes. So I bought a whole shoe store instead."

Fake sneakers used to be easier to spot

My friends and I at .IMAGE have spent two decades buying, selling, and authenticating shoes. We've built a collection probably worth over $1 million.

One of my favorites is this pair signed by Kobe Bryant, probably worth about $30,000.

I've handled hundreds of thousands of sneakers — Jordans, Dunks, Air Forces — and I'd say about 20% of those are fake.

Counterfeits used to be easier to spot, but these days, the fakes have gotten so much better.

Sometimes the only way to know is to bring them into a buy-sell-trade shop like mine. Even then, we have to get really close and look at every detail.

One of the most obvious giveaways is the color

Take the Jordan 4 Retro Red Thunder, for example. I'd estimate that about 80% of the time this shoe comes into our store, it's fake. I have no idea why this specific model is so popular among counterfeiters.

Right off the bat, you see that the tongue on the real pair is a darker red compared to the fake ones, which are a lighter red.

However, it can be the opposite case where the fake pair has a darker color, like with these white Air Jordan 4s. The toe box coloring on the fake is darker than the real version.

Shape and form are other clues

You can also usually spot a fake by looking at the shape.

For example, the tongue on this real Jordan 4 Retro Red Thunder is a little puffier than the fake one. The legit one looks like it would be cozier on your foot, too.

Other times, the real shoe will have a sleeker look. Like this white Air Jordan 4, if you look at it from the side, you can see that the real one has a pointy shape and structure, whereas the fake looks bulkier.

Smell, touch, and imperfections can be dead giveaways

We even smell the shoes because the fake pairs often use a toxic glue that's easy to detect.

Fakes also often use low-quality pleather, which feels stiffer. By comparison, the real pair feels soft and plush.

Ironically, real pairs often have little imperfections from the factory, but fakes are almost too perfect. That's actually a red flag. If it looks too flawless, I start getting suspicious.

Like these legit ones have a little glue mark that was a manufacturing mistake, but the fake ones don't.

Look at the box

Sometimes, it comes down to the box. For the example, the little dots on the real pair are more metallic silver than on the fake pair. The counterfeit is a little more solid gray.

Even the color of the red Jumpman logo can look slightly different. It's darker on the fake one.

Be wary of really popular models

These are the Air Jordan and the Travis Scott collaboration. This is one of the most counterfeited shoes because it's the most valuable on the market right now.

We have authentic pairs available to double-check any time this pair comes in. We make sure the threading is good and the sole color looks right.

The fake market is always changing and we have to keep up

We used to use black lights to catch where fake factories would mark the shoes for gluing or stitching, but the counterfeiters caught on and stopped using those markers. Now, black lights don't tell us anything.

Nike tried adding RFID tags to help with authentication, but guess what? The fake company would copy those, too.

Spotting a fake is not an exact science. Every day brings a new challenge. A new colorway hits shelves, and you have to relearn the signs.

These fake companies are making sneakers that are so good, sometimes a one-to-one replication, that the general public doesn't even know how to tell them apart. So you've got to come to reputable shops like ours.

We compare, cross-check, and trust our gut.

We don't want any fakes to leak out and hit the shelves because if a customer buys it and finds out, then our reputation is tarnished.

If I'm not sure if a sneaker is legit, I'll put it off to the side. I'm not even going to try and sell it. We've taken losses in the past to ensure our customers get a real product.

This story was adapted from Shu Cheng's interview for Business Insider's "Big Business" series. Learn more about Cheng and the counterfeit industry businesses in the video below: