法官面對不動產瑕疵衍生的價損爭訟時，會希望得到估價專業的協助，提供具有科學性質的參考數據。但是在一些法院判決中，法官表示不信任估價方法，甚至直言報告不符合證據能力的要求。本文以瑕疵建物價值減損為例，建構估價過程所依據的觀念以及程序，並且以實際案例呈現觀念的可操作性。評估瑕疵建物時，必須先謹慎地檢驗污名效果的顯著性。一旦存在污名效果的顯著性，建物瑕疵造成的價格減損，就應該包括修復費用以及污名價值減損。使用比較法時，污名是一個殘餘價值的觀念。污名價損的大小，端視瑕疵發生前之不動產價值、與瑕疵發生後修復後之不動產價值的價差而定。折現現金流量法中污名的價損效果，則是表現在提高的折現率。此外，成本法中的功能性退化，可以表示瑕疵造成的整體建物價損，並以重建成本與重置成本的差額代表污名價損。即使是門應用科學，不動產估價還是需要依賴經驗法則和有根據的猜測。但是「沒有什麼比一個好的理論更加實用（Nothing is more practical than a good theory）」這句話，終究是條應該堅守的底線。

Judges often need professional assistance from real estate appraisers in providing written evidence to facilitate a court decision in which the value of a defective building structure is disputed. However, some appraisal reports are distrusted by judges. In defense of the scientific nature of property appraisal, we suggest for a significance test of stigma effects on structure defect prior to undertaking an appraisal. Once the stigma effects are justified, primary appraisal methods can be applied with necessary refinement. When sales comparison method is employed, stigma shall be regarded as a residual of value. In discounted cash flow method, increased risk is deemed as a proxy of stigma represented by a higher discount rate. In the context of cost method, stigma is reasoned as a form of functional obsolescence estimated by the difference between reproduction cost and replacement cost. Real estate appraisal is often argued to be a combination of science and art. We however are opposed to this conventional thinking. Rule of thumb and educated guess are needed in appraisal, but they will not make appraisal an art.