India, Oct. 25 -- In May 2023, Jackie Crenshaw of East Haven, Connecticut, was nearing her 59th birthday and thinking about retirement when she met a man on a dating site who told her he was a widower, she said in an interview with Business Insider. He was a scammer, and a crypto romance scam cost her about $900,000. Now she works with AARP to warn others about the red flags she missed.

Jackie had a healthy 401(k) after years of saving about 15% of her income. She also wanted a companion to share her later life. A friend set her up with a profile on BLK, a dating site for African Americans. Jackie spotted a contractor there who called himself Brandon Miller. He told her he was a 49-year-old widower with two young boys. After two to three...