You Sir, are the real deal. I'll gladly buy stuff from you any day of the week.
Unfortunately, loads of stuff is sold by guys who are just looking to get rid of their bike/trainer/wheels or whatever, so they create an account just to post an ad, and disappear as soon as it's sold, which isn't evil or wrong. But those are very often the "problem cases". I don't think it's always intentional though. There are definitely some guys that are intentionally deceitful, but I like to think that in the majority of cases, people aren't being deliberately deceptive, they're just uninformed or don't know any better.
For example, I look at a drive train where everything is coated in black sludge from years of lubing without cleaning it, and think it must be toast and that there's a good chance I'll have replace half of it if I buy the bike, but to an unknowing owner, he just thinks to himself that he rode the bike yesterday and it all worked fine, so he writes "great condition" on his ad. A simple comment of "Hey bud, when last did you service the bike or replace the chain?" can help everyone that sees the ad know what they're buying, and can actually help the seller if he actually replaced the chain last week but uploaded old or bad photos.