How do you validate your property managers appraisals - Believe it or not

Really good topic. I have had all 3 roles: as Tenant, Owner and PM.
Do I believe my PM's appraisals? I hope I can but I couldnt in the past. That has to do with that person's strategy and approach. I find we always doubt their rationale, mind-boggling, so decided to take over the decision-making.
As a PM now, my ultimate goal is for Owners to go with the market flow. We advertise at the higher rate within the bracket, wait 1-2 weeks, and adjust accordingly. As a local, we know our area well, much better than the Owners themselves. Most Owners compare with past record but only for their own Unit. They do not have much idea about the adjacent area, which is most critical. As @Colin Rice said, some properties are unique and the PM need to know where they stand.
We have properties rented for $25 more than we thought they would, and another for $30 below the Owner's asking price. The higher rent was because it was a really nice Unit and the Tenants are quite fixed in moving into the area. Whilst the latter was a first time rental with a not-so-nice Unit.