Best way to make members aware of someone ripping people off in trading section?

Though true extenuating circumstances do occur that are legit. I venture to say the opposite happens way more often. Honesty,credibility , and a sense of fairness are fleeting traits in man kind. This has become more true since we got away from a penal system and embraced the bullshit idea that there is good in everyone and we can rehabilitate anyone! Sorry I digress.
fair enough - but for the most part the people on here are straight shooters - so I tend to expect and hope the answers to this kind of thing are less ill willed in nature