Originally Posted by
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It's still not even 100% known what Trust Factor is even based upon, and therefore impossible to give an estimate or even a gauge if it's moving at all in the right direction. From personal experience, playing many games without being reported over performing at extremely high levels nudges it strongly toward the green. I would wager hours doesn't actually affect it much, and that games played without issue affect it more.
Adding prime status through linking a phone number is confirmed by Valve to improve trust factor, as well as acquiring your rank after placement matches, so get on both of those. Best advice would just be to play as much as you can, as bought accounts almost exclusively drop heavily in trust factor (possibly an automatic system by Valve that detects a new account owner).