Key Takeaways
- Use only sold prices, never asking prices, for comp analysis.
- Always adjust for condition differences between comps and the subject property.
- Apply time adjustments in trending markets; limit comp age to 6 months in volatile conditions.
- Verify square footage independently—county records are wrong in 22% of cases.
After reviewing thousands of investor analyses and appraisals, certain valuation mistakes appear consistently. These ten errors collectively account for the vast majority of valuation failures. Each one has destroyed deals, eroded returns, or caused investors to miss opportunities. Internalizing this list is essential insurance against repeating the most costly mistakes.
Mistakes 1 Through 5
Mistake 1: Using asking prices as comps. Asking prices reflect seller hopes, not market reality. Only use sold prices, verified through MLS or county records. In a declining market, the gap between asking and sold prices widens dramatically. Mistake 2: Ignoring condition differences between comps and the subject. A renovated comp that sold for $350K is not a valid indicator for an unrenovated subject without a $40K-$80K condition adjustment. Mistake 3: Overestimating After-Repair Value. ARV projections frequently assume "best case" renovation outcomes. Use median comps, not the highest sale in the neighborhood. Mistake 4: Using stale data. A comp from 18 months ago in a market that has declined 8% requires a significant time adjustment. In rapidly changing markets, limit comps to 6 months or less. Mistake 5: Ignoring market direction. A comp that sold for $300K six months ago in a declining market at -5% annualized is only worth $292,500 today. Always apply time adjustments in trending markets.
Mistakes 6 Through 10
Mistake 6: Conflating assessed value with market value. Assessed values are updated on different schedules by jurisdiction (annually, every 3 years, or only upon sale) and may lag current market by 20-40%. Never use assessed value as a proxy for market value. Mistake 7: Cherry-picking comps. Selecting only the highest comps to support a desired price is confirmation bias in action. Include all relevant comps and let the data speak. Mistake 8: Ignoring external obsolescence. A property adjacent to a new waste transfer station, under a flight path, or next to a shuttered factory suffers external obsolescence that no renovation can fix. Mistake 9: Projecting rent growth without data. Assuming 5% annual rent growth because "rents always go up" ignores markets where rents are flat or declining. Use actual historical rent data for the specific submarket. Mistake 10: Not verifying square footage. County records are frequently inaccurate on square footage, sometimes by 10-15%. An unpermitted addition may not be included in assessor records. Always verify with your own measurement or survey.
Common Pitfalls
Relying on county assessor records for square footage without verification.
Risk: Mispricing based on incorrect size data can cause overpayment of $20,000-$50,000 on a typical residential property.
Measure the property yourself, hire a surveyor, or obtain a floor plan measurement during inspection. Compare against assessor and MLS records.
Projecting aggressive rent growth without submarket data.
Risk: Overstated projected income leads to inflated income approach values and underperforming investments.
Use 3-year trailing average rent growth for the specific submarket, available from Zillow ZORI or local rent surveys.
Best Practices Checklist
Sources
- Appraisal Institute — Valuation Standards(2025-03-15)
- CoreLogic — Property and Market Data(2025-03-15)
Common Mistakes to Avoid
Relying on county assessor records for square footage without verification.
Consequence: Mispricing based on incorrect size data can cause overpayment of $20,000-$50,000 on a typical residential property.
Correction: Measure the property yourself, hire a surveyor, or obtain a floor plan measurement during inspection. Compare against assessor and MLS records.
Projecting aggressive rent growth without submarket data.
Consequence: Overstated projected income leads to inflated income approach values and underperforming investments.
Correction: Use 3-year trailing average rent growth for the specific submarket, available from Zillow ZORI or local rent surveys.
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Test Your Knowledge
1.For The Top 10 Property Valuation Mistakes, which valuation approach is typically given the most weight?
2.How should investors handle conflicting results from different valuation approaches?
3.What role does market knowledge play in property valuation accuracy?