Whats the UK check scam

Notice that a buyer from the UK offers to purchase equipment. Is this a scam, please explain.
Send me a money order for $20.00, and I'll tell you all about it!
Maybe, probably not. With the sky high $ to pound exchange rate and general low cost of high end equipment in the USA, it is very tempting for Hifi enthusiast in the UK to purchase used equipment in the USA. If you want to find out if the deal is sincere, simply insist on cleared payment before you ship. It also helps to talk with the person before making any transaction of this nature. Just be cautious.