The ratings from a trust network don't really come from a computer, in some sense. It's just doing "provably correct" probability math on your ratings of other people and their ratings of information. So the computer can still generate wrong probabilities, if you feed it the wrong input probabilities, but to the extent that the input probabilities are correct, the output probabilities will be correct. It's similar to the situation where you use a calculator: if you feed it the right inputs, it will generate the right results, but that can be a "big if".

I have a hard time trusting a computer generated number.

Yes, and rightly so to some extent. For a system like this to be trusted, there'll need to be a lot of transparency surrounding the calculations it does. But I see those capabilities as very necessary anyways, since one of the important capabilities of a system like this will be the ability to identify when you're getting bad inputs that are skewing your results and ways to tweak your inputs to adjust its performance.