While browsing eBay for vintage finds, steer clear of anything that looks like it once graced an ancient tomb, temple, or palace. As The Wall Street Journalreports, up to 80 percent of antiquities on the online market are likely either looted or forgeries.

The illicit trade of antiquities is nothing new, and unscrupulous dealers and smugglers have plied their wares on the internet for years. But recently, there's been an uptick in fake or stolen artifacts sold on the web. Neil Brodie, a senior research fellow in endangered archaeology at the University of Oxford, estimates that at least 100,000 antiquities are listed for sale online on any given day. Collectively, they’re worth more than $10 million, according to the Journal.

This boom could be chalked up to a variety of factors, including the growth of social media and e-commerce platforms and the large-scale plundering of sites in Syria and Iraq. Groups like ISIS sell these stolen antiquities to collectors, and use the proceeds to fund terrorism and criminal activity.

Thanks to social media, it’s easier than ever to sell illegal goods directly to potential customers. But in addition to potentially funding terrorist activity, there’s a good chance that collectors' objects of desire are either illegal or fake, as an estimated 80 percent of the so-called antiquities have sketchy provenances, Brodie said.

Tech giants like Amazon, Facebook, and eBay all forbid the sale of stolen objects, and they also remove suspect ads, content, listings, and even users. But overall, regulation is lax, although heightened scrutiny by international organizations and officials might prompt these companies to take extra security measures.

eBay—which sells five collectibles per second, according to Artnet News—is reportedly trying to thwart trafficking by providing customs officials with the identities and contact info of suspicious sellers. Experts have also suggested that the e-commerce company adopt other anti-trafficking measures, like posting prominent warnings about stolen or fake goods on the site. Meanwhile, undercover agents have taken to monitoring apps and websites in search of potential criminals.

For now, if you're a collector, you can help by ignoring those ads for "uncleaned" ancient coins that look like they’ve just been dug up. Both your wallet and conscience will thank you.

[h/t The Wall Street Journal]