Basically with the new Trust system, Valve will be giving players a “Trust Factor”. This will see the developer take into account your behavior based on other games that they have in their Steam account, and how often they might have been reported for cheating, and so on. The idea is that if you have a history of cheating in other games, it wouldn’t be a stretch to think that you could cheat in CS:GO as well.
According to Valve, “We wanted to keep the best parts of Prime and ditch the parts that cause problems in the CS:GO community. Starting today, players will, by default, enter matchmaking using their Trust Factor rather than their Prime status and in the short term, players with Prime status can still choose to match using the old system.”
As for what is the criteria you will be judged on, it appears that Valve is keeping mum on that front, which we guess makes sense since they probably don’t want players to try and game the system. So far the company is claiming that the results of their experiment have proven to be positive, but we guess we’ll have to wait and see what happens in the long-run.