Sadly, you can have 10 good encounters and one bad one but it's the bad one we generally remember.
It's not just the traders, sometimes it's the law enforcement as well. So eager to catch you and get their little blue message that they tend to ignore the little things...like the rules for example.
One day I'll learn to get that video capture thingy working.
If I get a piss poor experience that winds me up, I generally walk away from the PC or change game for a couple hours. Especially when they say "Yeah, I did but so what"?
In case your wondering, yes, it has just happened.