I know as a newbie interested in customizing your trust list it's kind of difficult if you haven't traded with any user to trust their judgement or familiar with the active scammer busters
From previous threads on this topic, I understand that a custom trust list does not comprise of people who you trust in trades, but members whose judgement you trust and recognize their ability to make important decisions without bias or prejudice.
For members you trust you can leave a positive feedback.