Ever wondered how a top investor can tell if a startup founder is the real deal? Instacart co-founder and seed investor Max Mullen has a surprisingly simple trick — and it all starts with a glance at their feet.

In a recent podcast, Mullen shared that after backing over 100 startups, he’s learned to spot the true builders by looking down at their sneakers.

The Dirty Sneaker Test

“If you’re looking at a founder and they got dirty white sneakers,” Mullen said on the “Uncapped with Jack Altman” podcast, “you’re a real builder.”

His logic? The entrepreneurs who aren’t obsessing over their appearance are the ones sleeping at the office and working around the clock. “They don’t have time to buy nice sneakers,” he explained. “They just put on the same pair of sneakers, and they get dirty.”

Mullen even invested in the AI automation platform Gumloop after noticing one founder’s shoes were “falling apart.” He was so convinced that he bought the founder a new pair. “My cofounder Rahul does not see the purpose of buying new shoes or shirts, so Max bought him a new pair,” Gumloop’s Max Brodeur-Urbas told Business Insider.

What It Really Means

In contrast, a founder with a perfectly dialed-in aesthetic is often “signaling that they’re a great founder rather than spending every ounce of their energy becoming one,” Mullen wrote in a blog post. For him, the real builders look the part — and that part is often a pair of dirty white sneakers.

So next time you’re pitching an investor, you might want to skip the shoe shine.