Shares of the payments company formerly known as Square fell about 15% on Thursday after a short seller questioned the company’s user numbers and accused it of predatory tactics. Hindenburg Research said a two-year investigation into Block found the company “obfuscates” its Cash App service’s true user numbers by reporting misleading metrics “filled with fake and duplicate accounts.” It also accused the company of taking advantage of the demographics it claims to serve—lower-income people and minorities—with “predatory loans and fees.”