I had exactly the same thing happen to me selling a Porsche on Autotrader. It is impossible for these web sites to screen everything. Scammers keep coming up with new ideas. You you did a great job picking up on it. When dealing with people you do not know always do so with distrust until you get to know them. It is one of the reasons I hardly ever ship. Local pick up only. If someone really wants something they can come and pick it up. People who are going to meet you face to face are much less likely to scam you. The young man that just bought my old Sota handed me a wad of cash. I never asked for cash only. It was understood.
Craigslist Fraud
Just thought I'd share my recent experience with attempting to sell some audio equipment on Craigslist. Attempted to sell a Audio Research Ref 3LE. I know now that doing so via Craigslist was probably stupid. Anyway, I had a guy from out of state reach out to me. Said that he wanted to buy it. Asked that he send a cashiers check. A couple days later the FedEx arrives with a check for $12K more than what I was asking... The alarm bells went off. Check was from a business in Chicago and the FedEx was from Florida. They did a very convincing job of making up the check. Reported it to the police - so I could feel better. They let me know that the scammers would probably have come back and asked that I send part of the money back to them.. as if. Rang the company that the check was reported to have come from (The Belt Railway Company of Chicago). They said that I was the 6th person in the last week that rang them. Wanted to put this out for y'all and hope that no one goes through this like I did. Very thankful that it only cost me time, frustration and some dents to my ego.