Pardon my ignorance, but I see his trust rating is:
-7: -2 / +0(0)
Warning: Trade with extreme caution!
How do I find out more about the situations that led up to this? When this warning is added to someone's profile is it due to a particular thread/discussion involving moderators?
It's because he has been constantly spamming that TF is a scammer with next to no proof, as well as using the accusations of scammer-tagged people to call him a scammer. Those are member-given ratings (from me and TF, actually) and you can see the references if you click the Trust button.