Do you know how I know this? Craigslist.
I understand that times are tough and you may not want to buy the home theater system I'm selling, but if you send me an email and tell me your interested and we go so far as to negotiate the price, and you end up changing your mind, at least have the courtesy to fire off a quick message back to me to let me know, instead of just disappearing...never to be heard from again.
This has happened three times.
I'm not even going to go get started on the scammer who wanted me to ship the thing to Europe, with the promise of paying full price once it was in transit. I'm not stupid enough to actually fall for that one.
Screw it. I'm donating to Goodwill.