Summer is a high season for housing buying and selling activities. Many buyers and sellers use online valuation site to get an idea of how much the house they want to buy or sell worth. While they could give you a rough idea, you need to be very aware of their limitation and these values could be very off many times.

Here are insights from Tara-Nicholle Nelson who is an author and the Consumer Ambassador and Educator for real estate listings search site Trulia.com on why they do not work: 

What’s involved is a computer taking the description of your home from the public records (which usually reside at the county recorder’s office and in their databases) or from a recent listing (if your home has been sold in the past few years), in terms of the number of bedrooms, bathrooms and square feet, primarily, and pulling out the closest homes to yours that have sold recently that have similar data on record.

However, the computer can’t necessarily distinguish nuances in a property’s condition or aesthetics, nor does it always correct for whether the house two blocks over was a short sale or a foreclosure.

Depending on where you live, how similar homes are to each other in your area, the level of sales activity near your home and the level of accuracy found in the public records for your house and nearby homes, these sites can offer very comparable “comps” — or comparables that aren’t really comparable at all.

If you live in a fairly cookie-cutter subdivision where several homes just like yours have sold very recently, you’re likely to get a good set of comparables, and a value estimate that’s at least in the ballpark. But in many areas, lots of fairly common scenarios can come between you and a good set of automated comps:
• if your home is older and has had a lot of improvements and even additions that are not in the county records, you’re likely to get bad comps;
• if homes in your area are very different from each other, you might get bad comps;
• if you live in a neighborhood very nearby another neighborhood where homes have a much higher or lower value than your area’s (say, because they belong in a better school district or even on the other side of the city limits), you’re prone to getting bad comps;
• if your home is in an area where homes are dense, the algorithm might jump over many very nearby properties to get to a relatively dissimilar one even a half-mile away, and that can give you bad comps.

The listings provided by the sites can be very useful for homeowners trying to stay on top of what homes around theirs are selling for — not listed for, but actually selling for. They are less useful, in my opinion, at placing values on properties; the sites that do this usually have their accuracy rates listed somewhere on the site, and I haven’t yet seen one that’s impressive.

But when it’s time to actually list your home, or figure out what it is worth, no computer — no algorithm — is as accurate as a living, breathing local real estate professional who sees and sells all the different specimens of homes in your neighborhood and sees firsthand what ready, willing, qualified buyers actually pay for them, day in and day out.

I think it’s important for sellers interviewing listing agents to discuss the online comparables with prospective listing agents, but not as a counterargument to what the listing agents recommend you list your home at.
Rather, it’s a smart way to see what the agents know — and what you can learn — about the other properties in your area.