Estate agents tend over value to get business and they often over estimate the buoyancy of the market. Their job relies on the market being fast moving. But in a fast market they have the best insight. Especially into specific areas.
Surveyors take account of condition but relie on stats for market condition. These can be out of date or not take account of certain market drivers, like proximity to schools. But they are professional and trained and they do use data to back up their valuation. They can be conservative. However hidden faults that the new owner will need to address are factored in.
A property is worth what someone will pay for it. That’s our system and markets are very locally sensitive and often volatile.
Getting estate agents quotes to understand the approximate value is ok at certain stages of the divorce. It’s ok advice if the value will be split by %. It can be the wrong advice if one party is getting a fixed amount and there is no independent buyer and if this is going to court.
If one of you is buying the other out then you are most likely remortgaging and the surveyors report is being used. That adds weight to it being the default value. But it doesn’t mean someone couldn’t show it is wrong. I mean you can appeal mortgage panel decisions based on the survey price.
If you house is atypical or unique and there aren’t many comparables the valuation can be unreliable no matter who does it. If you house is identical to every other house in the area and in standard condition then recent sales data will be a good indication.
The bottom line is that estate agents and surveyors have conflicted interests. As do you and your ex. Unless you agree it is a judge you will need to convince. They will look at valuations from both and any information either party presents to challenge these. Then it is up to the judge.
Yous should both do you own research and then present it to each other. It is easy to establish market price v sold price for the estate agents. It is usually about 5-10%. Surveyors are usually about the 5% behind the market. If you have very recent comparables in your immediate local area use them.