You bought a Smartphone (iPhone, Blackberry, or Android) and you are excited about it. You were offered a warranty (just in case you break the phone and need to replace it), but you figured you were spending enough so you opted not to take it. That's not always a bad idea, but it was for you—one day, the unexpected happened.
You now have to spend hundreds of dollars to replace the phone! You want to try and buy a bit smarter, so you look into an online auction for an unlocked or "jailbroken" phone, which means you can use it with any carrier. You find a phone for half price and you swoop it up, patting yourself on the back for making the best out of a bad situation.
Unfortunately, you didn't. The phone never comes and you now have to pay hundreds more dollars to finally get this ordeal sorted out. Reports suggest that 80% of people selling cell phones online are scammers.
How to avoid: if you're using eBay, check on the feedback they've gotten so far. If it isn't really good, or there aren't enough of them, just check all the other thousands of great deals that eBay and Craigslist. Find someone who is verifiably trustworthy.