Although this is a beginner's guide, you may find it a little difficult to understand at first. A trust system is established to make the forum as safe as possible against scams and untrustworthy people.
I have a simple understanding of how I should trust someone to be on my trust list. Most of the DT1 members can be trusted by me, but not all of them I can trust when I review the reputation they have earned over the years. I trust their reviews especially on cases involving other people's reputations, but I might edit that list if in the future I get something different about them.
OP, simply put, trust someone you deem worthy based on their reputation and contributions and it's not limited to trusting someone you know in real life even if they don't trade with you. The problem so far, some users are scratching themselves, has been discussed a lot lately.
