Data Collection: Comparable Sales, Public Records, and MLS

Why Comparable Sales Data Quality Matters

Every residential appraisal or comparative market analysis (CMA) rests on the quality of its comparable sales. Garbage in, garbage out: if your sales data is wrong, your value conclusion is wrong, and a client, lender, or court may rely on it. Accuracy is a professional and legal obligation. Both the State Real Estate Salesperson License and the IREM CPM credential assume you can locate, retrieve, and verify sales data responsibly.

The Three Primary Data Sources

Multiple Listing Service (MLS)

The MLS is a cooperative database maintained by a local or regional association of REALTORS®. It contains active, pending, and sold listings entered by member agents. MLS records are rich in property characteristics—square footage, bedroom and bathroom count, lot size, year built, and photos—but they are entered by humans and can contain errors or omissions. MLS sold data is the starting point for most residential comparable searches because it is fast and detail-rich.

Key limitation: MLS data is self-reported by listing agents. It is not a legal record of anything. Always verify against public records before using a figure in a formal report.

County Assessor and Recorder Records

The county assessor maintains property characteristic cards (assessor cards or parcel records) and calculates assessed value for tax purposes. The county recorder (sometimes the same office, sometimes separate) maintains deed records that document every transfer of ownership. A recorded deed is the legal evidence that a sale occurred. It shows grantor (seller), grantee (buyer), recording date, legal description, and—in many states—the consideration (sale price), either directly or through a transfer tax notation.

Key advantage: Recorded documents are public record and carry legal weight. A deed's sale price or transfer tax notation is more authoritative than an MLS entry when the two conflict.

Commercial Data Aggregators

Services such as CoStar, CoreLogic, and similar platforms compile deed data, MLS data, and assessor data into a single searchable interface. They are powerful for pulling large data sets quickly. However, they are only as accurate as their source feeds and update schedules. Always trace a figure back to its original source document before relying on it.

What to Record for Each Comparable

For each sale you locate, document the following fields on your standardized data sheet:

• Grantor (seller name as on the deed)
• Grantee (buyer name as on the deed)
• Recording date (date the deed was recorded, not necessarily the closing date)
• Sale price (verified from deed, transfer tax stamp, or MLS disclosure)
• Property address and parcel number (APN)
• Property characteristics: gross living area (sq ft), lot size, year built, bedroom and bathroom count, garage, condition
• Data source (MLS, deed, assessor card, commercial database)
• Verification method (how you confirmed the figure)

Never leave source or verification blank. If you cannot trace a data point to a specific document, flag it as unverified.

Selecting Sales: The Twelve-Month Window

Industry practice for residential CMAs and appraisals generally calls for sales within the past twelve months from the effective date of the analysis. Prefer the most recent sales first. Six comparables is a practical minimum; eight to ten gives you room to bracket the subject's characteristics. Focus on properties in the same neighborhood or competing area with similar size, age, condition, and use.

Verification: Cross-Checking MLS Against Deed Records

Verification is the step that separates professional-grade data from casual internet searching. The process:

1. Pull the sale from MLS and note every data field.

2. Search the county recorder's index by address or grantor/grantee name to locate the deed.

3. Compare the sale price on the deed (or calculated from the transfer tax) with the MLS closed price.

4. Pull the assessor card and compare the property characteristics (square footage, year built, bedroom count) with MLS.

5. Note every discrepancy in writing.

6. Identify the more reliable source for each discrepancy. Deed recording date and consideration are more reliable than MLS. Assessor card square footage may reflect a prior permit record, not a recent addition—use judgment and note the conflict.

7. Write a reconciliation memo explaining which figure you used and why.

Reconciliation Memo Format

A reconciliation memo need not be long. One paragraph per sale is sufficient for this exercise. State: (1) what conflict you found, (2) which source you judged more reliable and why, and (3) the figure you will carry forward. Example: "MLS shows a closed price of $X; the recorded deed transfer tax notation indicates a consideration of $Y. Because the deed is a legal instrument recorded under penalty of law, I am using the deed figure. The MLS price appears to have been entered in error."

Data Integrity and Confidentiality

MLS rules prohibit sharing access credentials. Log in only with your own school-provided credentials. Do not export or distribute MLS data beyond what your subscription and the association's rules permit. County recorder data is public record and may be freely used. Handle any personal information (buyer and seller names, addresses) with professional discretion—this is not gossip material.

Accuracy Is Non-Negotiable

In a formal appraisal or CMA, a misreported sale price, wrong square footage, or unverified data point can mislead a lender, harm a buyer, or expose a licensee to disciplinary action. Develop the habit now: source every number, verify every number, document everything.