Shortly after he answered a call from an overseas number, Henry Guo, a retail worker in Shanghai, said he was contacted by local police. They told him it was a scam call and requested an in-person chat.About ten minutes later, law enforcement officials showed up at Guo’s home and asked if the 37-year-old had transferred any money to the caller. They left after he signed a document attesting that he didn’t take any actions that could make him a victim of a financial scam....