Until recently, residential property transaction data was largely unavailable within the UK. Therefore, determining the impact of a detrimental condition, such as high voltage overhead power lines (HVOTLs), on the value of residential homes relied on the opinions of appraisers. However, when asking price is compared with transaction data for the same location the trend is reversed and appraisers were often found to underestimate the real impact on value. This paper suggests that when dealing with a detrimental condition where transaction data is scarce, the use of a multi-method approach may improve the reliability of findings; however, such results should be treated with caution.