For the most part, I find people (esp. on Audiogon) go out of their way to be explicit about what they're selling and what condition it's in. I've been very satisfied in most of my transactions. I've had minor disappointments in more than one transaction - gear that is a little more scuffed up than advertised, etc. I've only had one purchase where something that was advertised as "perfect condition" had a malfunctioning feature - I worked with the manufacturer and got the piece needed from them (for free) and a friend repaired it, at which point it was "perfect condition". I've never encountered the type of seller horror story you occassionally read about.
I find the percentage of the time I encounter this type of behavior to be small enough to not push me away from this type of transaction, but anybody doing this type of purchasing has to factor the possibility into their expectations because you can lose a lot of sleep if "minor" mis-leadings are going to really get under your skin. -Kirk