The only problem I see with this system is the top xx people will continue to gain more trust and will pull ahead of the rest of the users. You're basically replacing the DefaultTrust with those people.
That's my opinion as well, although I concede it's an improvement over the current DefaultTrust as people will have to manually choose who they trust. I'm not sure how randomizing the list helps though, since the page will be displayed only once.
Instead of showing always the 30 best scorers, an alternative would be to show some random 30 among the 50 top, so people blindly ticking all the boxes don't end up trusting the same set of users.