> trust-based systems only work if they carry risk. Your own score should be linked to the people you "vouch for" or "denounce"

This is a graph search. If the person you’re evaluating vouches for people those you vouch for denounce, then even if they aren’t denounced per se, you have gained information about how trustworthy you would find that person. (Same in reverse. If they vouch for people who your vouchers vouch for, that indirectly suggests trust even if they aren’t directly vouched for.)