Almost every bad trade I've seen over the years comes down to one of three things:
1) Impatience;
2) A compulsive need to tinker; or
3) Over-reaction to criticism.
Here's my advice: don't make bad trades. Ever. If you don't like the value you're getting, don't trade. It's seemingly common sense, but lots of great GMs make silly decisions. Shop around. Don't make a trade until you've talked to at least 20 other GMs. Make counter-offers. Be patient. Lastly, don't overthink things, especially if the seeds of doubt were planted by a competitor.