Mercari, a mobile e-commerce site that matches individual buyers and sellers, has banned sellers from listing cash after the site operator discovered that ¥10,000 notes were being sold at a higher value.

According to officials of the Japanese startup virtual market place, which mainly deals in used items such as clothing, those cases indicate some sellers were trying to take advantage of the e-commerce site and capitalize on people desperate for immediate cash.

Under Mercari’s transaction system, buyers can pay with credit cards. For people in desperate need of quick cash, paying ¥13,000 for a ¥10,000 note had merit, the officials said.

Such cases started increasing in mid-February after Mercari allowed users to sell currently circulating coins and paper money in addition to old money and collectable coins and bills.

The move came in response to users’ requests that coins minted with errors, such as a ¥5 coin with a misaligned hole, are rare items with added value.

However, such deals could lead to financial trouble among users and in the worst case become a hotbed of crime. Thus, Mercari has banned such deals since Saturday and is deleting them from the site if found.

Dubbed the “flea market app,” Mercari has proved popular since its launch in 2013 for its simple transaction procedures compared with online auction sites like Yahoo Auctions. Mercari, which is mainly provided as a mobile phone app, has been downloaded 40 million times in Japan.