Seven times last month, Benjamin Karmis, a 26-year-old priest from Wheaton, Illinois, failed to get his hands on the latest Sony PlayStation 5 video game console from retail websites including Walmart Inc and Facebook Marketplace.

But it wasn't because another person beat him to the purchase.

Instead, Karmis and other shoppers were outgunned by so-called “scalper bot” software, which resellers use to snatch up products online and relist them moments later at significant mark-ups on eBay and Amazon Marketplace.