Isn't that "some other" people is a tender spot cus they can divulge the private information?
Well it's always a human factor in some way. But most of the projects just can't be verified any other way. For example a project relied to administrating can be working properly "on paper" but it won't work in real life conditions.
Also want to mention that in most of the situations verification agents are receiving only a part of the whole information and that reduces the chance of a leak.