Every homeowner in Rockwall County has a number in their head, and most of them got it from a website. The websites are not hiding how accurate that number is. This post puts their own published figures next to what an agent's valuation does differently, explains what Texas law says an agent may and may not call that valuation, and tells you when neither is enough and you need a licensed appraiser.
What the estimate says about itself
Zillow describes its Zestimate as an estimate of market value built from public records, MLS data and user-submitted details, and states that it is not an appraisal and cannot be used in place of one. As of its September 30, 2026 refresh, the nationwide median error rate is 1.77 percent for homes on the market and 7.20 percent for off-market homes. Zillow's definition: for listed homes the estimate is within 1.77 percent of the final sale price half of the time, and within 7.20 percent half of the time for off-market homes. For Dallas-Fort Worth the on-market figure is 1.81 percent, with 86.51 percent of listed homes within 5 percent (Zillow, What is a Zestimate).
Read that carefully. The on-market number is good because the model has the list price, the photos and the pending status to work with; it is largely tracking the price the listing agent already set. The off-market number is the one that applies to your house before you list it, and a median error of 7.20 percent means half of all off-market homes are off by more than that. On a $600,000 home in Rockwall, 7.2 percent is $43,200 in either direction, and that is the median, not the worst case. Zillow itself says accuracy depends on the depth and quality of available data for the location and property (Zillow).
What the model cannot see
An automated model works from records. In this county the records miss the things that move price the most:
- The lake. Whether a lakefront lot holds a take line sublease and a permitted dock is not in the appraisal roll in a form a model reads, and two identical houses on the same street price very differently because of it.
- The lot. Heath's one-acre minimum for new development and its three-acre estate districts mean lot value is a large share of price there, and the model's square-footage comparisons underweight it.
- Interior condition and updates. Zillow's own FAQ says unreported additions, updates and remodels are not reflected in the estimate and asks owners to report them to the tax assessor (Zillow). A 2024 kitchen is invisible until someone walks in.
- The subdivision line. A model draws comparables by distance. An agent knows that a sale across the street in a different HOA with different dues, or in a MUD with a higher tax rate, is not a comparable. Our Stone Creek and Woodcreek guides show how much varies within a mile.
- The school zone. Rockwall ISD redraws attendance zones when campuses open (Rockwall ISD, attendance zones), and buyers pay for the zone, not the district average.
- Timing. A model reports what sold. An agent knows what is pending, what fell out of contract last week and why, and what is about to list next door.
What Texas requires the valuation to say
An agent's valuation has a legal name. Under Texas Real Estate Commission rule 535.17, a license holder may not perform an appraisal or provide an opinion of value unless licensed or certified as an appraiser. What an agent provides is a broker price opinion or comparative market analysis, and it must carry a written statement, verbatim and in at least 12-point type, that begins "This represents an estimated sale price for this property" and says it is not the same as the opinion of value in an appraisal developed by a licensed appraiser. A sales agent prepares it in the sponsoring broker's name, and the broker is responsible for it (22 Texas Administrative Code 535.17). The Texas Appraiser Licensing and Certification Board draws the same line: a broker's price opinion is an estimated sale price, not an opinion of market value, and appraisals can only be completed by a licensed or certified appraiser (TALCB, appraisal, evaluation and BPO).
That disclaimer is on every valuation the team delivers. It is also a fair description of what we are doing: estimating the price the market will pay, not certifying a value for a lender or a court.
What our valuation includes
- A walk-through of the home, with the updates, the condition and the things a buyer will object to written down.
- Closed sales from the same subdivision or the nearest true comparables, adjusted for lot, condition, pool, garage and view, with the adjustments shown.
- Active and pending listings, because they are your competition, and expired listings, because they show what the market refused.
- Property-specific factors: HOA dues, MUD or PID rates, the school zone, any take line sublease, easements and flood zone.
- A price range and a recommended list price, with the reasoning, and a net sheet that shows what you keep after the costs our seller's guide describes.
- The required TREC statement, in full.
It is free, it takes a visit and a day or two of work, and there is no obligation to list. Start at the valuation page.
When you need an appraiser instead
A comparative market analysis is the right tool for setting a list price or testing an online number. It is the wrong tool for anything that needs a certified value: a lender's loan file, an estate or divorce settlement, a property tax protest that goes to a formal hearing, or a dispute between co-owners. Those need an appraisal from a licensed or certified appraiser, which must comply with the Uniform Standards of Professional Appraisal Practice and is used in mortgage finance transactions and court proceedings (TALCB). If the appraisal district's value is the question, our homestead and protest guide explains what to bring to the review board; an agent's comparable sales are admissible there and we provide them.
A fair way to use both
Look at the online estimate. Note its range, which Zillow publishes alongside the point value and describes as the span of prices the home could reasonably sell for (Zillow). Then get a valuation from an agent who has sold in your subdivision, and ask them to explain every adjustment. If the two agree, you have a price. If they disagree, the one that can show you the comparables and the walk-through notes is the one to trust. Ask us for ours through the valuation form or a call, and read what past clients said on our reviews page first.