I think it's extremely fair to not trust people to evaluate themselves when doing open hiring - for networked candidates you can usually relax some assumptions and for very senior/niche positions there's usually ample street knowledge available... but in these cases you're relying on a third party for some level of vetting. I would never solely trust a second party during hiring unless I had some method to confirm at least some of what they're saying.

A lot of companies are far too hesitant to trust employees, but blind trust is unwise - you can end up with an employee that either wastes three months salary or actively causes damage.