When you hear that a 22-year-old makes his living as a dealer in marijuana, you probably assume he's illegally selling cannabis. But for Ben Milstein, the only thing he's buying and selling are expensive bongs.

Business Insider recently published a profile of Ben Milstein, who operates a business known as Grey Space Art. Milstein buys and sells expensive bongs, but they're hardly the kind you'll find in the homes of most stoners. Instead these are extravagant sculptures that can cost as much as $300,000.

Milstein doesn't just buy and sell his wares. He's opened pop-up art galleries in major cities across the United States to showcase his expensive bong collection. He's collected more than 500 pieces created by more than 80 artists as part of his business.

Since May, Milstein has made over $350,000 selling his bongs. But he doesn't plan on getting rid of his entire collection because he believes it needs "to be seen by more people."

After high school, Milstein invested in marijuana stocks right before it became legal in Colorado. Needless to say, his shares boomed. He worked briefly for an advertising agency before moving into his current bong business, although that's not how he would classify it.

"I'm not selling bongs — I'm selling works of art," he says.

If you want to know about Milstein and his business, head over to Business Insider.