LPT: When selling something online, take a picture of it right before you package it for shipping.

The lady I sold my flat screen TV to tried to tell me I sold her a broken TV. Thankfully I had taken a picture proving it was in working condition the day I packaged it, so something unfortunately happened during shipping and I was in the clear and able to keep my money.

Doesn't help the person on the other end, but it's nice to make sure you've got a safety net for scammers.