1. Vouches : When looking at the vouches, always remember that quality is more important than quantity. Consider this: one trader has 100 vouches, for 10 million each (The amount that was traded, this could be anything: GP, accounts, questing, skilling, etc.)
A second trader has 1000 vouches for 1 mil each, which one would you trust more? You are better off trusting the first trader since he/she has traded and handled more at one time. You should also consider if they used a MM/OMM, went first or second and what the trade was for.
2. Rank : A user that has earned the rank of Moderator/Administrator/OMM could be trusted a lot more than a regular user. That being said, users can be trusted more than people with ranks but with all I said you need to consider all factors. This should be the 2nd thing you look at to determine their trustworthiness.
3. Donation Status : If someone has donated not only does it show that they supported Sythe but it also gives them a little trust points. The reason I say this is why would someone scam $50 if they donated $100? However some scammers use previously stolen money to donate, so this should be the 4th thing you look at to determine a trader's trustworthiness.
4. Post Count : High post counts shows they spent time on Sythe and are less likely to waste it on scamming. Beware though this should be the Last thing you look at to determine their trustworthiness. Scammers usually spam their post count up to give themselves false trust
5. Join Date : If they joined this month I would be wary of them and if they joined a long time ago I would give them a little more trust points . Note: some scammers who legitimately traded years ago come back and are now using their "trust" to scam. This should be the 3rd thing you look at to determine their trustworthiness.