The mishna, K'subos 11:5, quotes Raban Shim'on ben Gamliel as saying that a court's property assessment is effective even when found to be far off the mark. The reason he gives is "otherwise, where's the court's power?". I fail to understand this. Why are we interested in boosting the power of the court in this regard? I can understand we want the court's decisions to have teeth, but that's in regard to decisions of guilt, innocence, liability, lack of liability, etc. If the court is not believed in such decisions, people will adjudge cases privately and anarchy will reign. But if the court is not believed in assessments, people will assess property privately and… so what? We don't mind people's assessing property privately, do we? Why do we need to enact a safeguard for the court's power?