Advance fee fraud.
A few years ago I was selling some industrial surplus on CL and got those all the time. I ****** a fe wof them around a bit to waste their time, and decided to see how far I could take it. I got one idiot to send me a fake check, which I sent to the postal inspectors office along with all of the information I had. All communication was by text messasge, with him using some web service called Textmail. I trolled this idiot for well over a month, and even got him to send a second check when I claimed that I never got the first one. I told him that I had to drive to another city to cash the check and get the money wired, and then didn't talk to him for three days. All the while I got a bunch of panicked emails from him. After a few days I responded claiming to by my niece. "Oh, Glen had a bad accident and he's in a coma. He was driving to the city to handle some financial matters and got in a bad wreck on the way. I'm his niece and I'm handling his affairs for now."
Acting as the "niece", I told him that I was handling all of his on line sales and asked what it was he bought. "Uh, I think it was a boat." It was actually a 3 phase power convertor that I had already sold to someone local for cash. After berating him, I suggested just giving him a full refund. He asked about a direct deposit to a bank account. "Yeah, please give me a way to trace you!" I agreed and he gave me a name, address and bank account number to make the deposit.
The address was in New Jersey, so I called the FBI office there with the information. This was in 2016, and apparently they were too busy investigating a particular presidential candidate to be interested in actual crimes, so they blew me off. I tried calling the FBI office in LA and they told me to file a report with the local police. After going back and forth with these idiots, I called Wells Fargo with the information and they weren't interested either. I guess they didn't care about a possible case of identity theft or a criminal gang using their services. After telling the guy at the local post office about it, he suggested getting the postal inspectors involved, and the guy I talked to there sounded excited at being able to investigate something like this. I led the guy on a few more days before blocking his number.
The name I gave him was Glen Milstead, and I really hope he tried to look me up on line. Go ahead, look him up IF YOU DARE...