Hey guys.
Warnings on user profiles (like this one: http://deckbox.org/users/GreyCr0ss) are indeed manually set by us.
I've also responded to the other thread, but I'll post here as well: send us an email at support@deckbox.org. If from your description it is obvious that your trade partner is scamming you, we will send him an email asking for an explanation. If he does not respond, we will mark his profile.
We do not over analyze situations, normal trade problems should be solved with a negative rating. Only in obvious cases we will mark a users' profile.
The next release we will add a "Report User" button to facilitate this kind of feedback, but we still do not plan to do detailed trade mediation, we hope the feedback system would take care of it. We also will put more details and information in the trade guidelines page.