They are pretty poor. They take a chunk of the fee generally negotiate on behalf of the buyer not the client to get a quick sake and have very little marketing knowledge
You can now see what houses have sold for so if there are properties sold in the area of similar spec you will get a idea
I sold a house a few years ago and the valuations were bizarre - highest was 75% higher than the lowest
I don’t personally think it’s him that’s looking silly - you keep saying facts are facts but are relying yourself on the word of a third party who I assume did not go to the actual protest