Below is an excerpt from a podcast script I came across, which talks about how you can fall for scam through emails and messages, and I don't understand the "check" reference they mentioned.
This is something I would say to my mom. "Beware there's this scam out there. Don't fall for it." I actually tested my parents once. Because they were selling something on craigslist, I sent them an email that said, "hey, I wanna buy it, I'll send you this check for more, if you can refund me the difference"... and my parents fell for it!
I'm having difficulty understanding the part in bold, especially "for more", and "the difference." I want to write more specific questions, but I'm not sure how to elaborate it. "for more" (what)? What does "difference" indicate? Maybe it's not about the words but about how checks work in the US that I'm not familiar of, but I'm completely lost interpreting this sentence.