That's simply not true. I myself have on many occasions commissioned estate agents to perform property valuations in Revenue audit cases, on the explicit basis that the valuations would be used as evidence in the course of the Revenue audits.
I've also known of and dealt directly with situations where estate agents have been subpoenad to appear in court to explain and justify to a judge, valuations they have made.
Any valuation is worthless unless the person preparing it is willing to stand over it.