Do people even perform trades again in order to have positive trust? That was when the forum was created newly and possibility there were little/no exchanges, so members of this forum were trading between themselves.
If you want to be in DT, just start accusing people of alt accounts, start connecting people's addresses, start bursting cheating bounty hunters and you would be surprised how fast you will be on DT.
That's too much work, just buy a Collectible and use (pay!) escrow, then leave both of them positive feedback. Changes are you'll get 2 positive feedbacks in return, and you'll be on DT2.
Note: I don't consider this correct use of the Trust system, but this has happened many times.