Beware estimates of value of sites like Zillow - they go FIVE miles to calculate their numbers which punishes the preferred areas and rewards the less desirable. They also do not take view, waterfront location or other valuable property features into consideration.
Others have addressed the (almost) real time updates of MLS comps available to Realtors. Let me talk about the listing process, and some of the other aspects of using comparable sales.
You mention that you want to list your home, but you didn't say whether you have spoken to any agents yet. An agent speaking to you about listing your home should be prepared with comparable sales, and should be capable of taking you through what they mean for the pricing of your home. Some agents will come to the first meeting with a full CMA worked out for you. My preference is to come to that first meeting with a general picture of past sales in the area, get a detailed picture of the positives and negatives of your specific property, and then come back with an analysis of the closest comparables and a pricing recommendation. Either way, an agent who cannot speak intelligently to the comps may be someone you don't want to use.
The first question you need to ask about a comp is whether the sale is truly comparable to the home you are considering (either as buyer or seller). Factors which might rule out an otherwise good comp include location (even within the same town), property size, property condition, upgrades the seller may have made, and damage or environmental issues. While it is possible to make adjustments for these factors, you are often better off finding a more suitable comparable when possible. For example, if you have a 1,500 sf 4 bedroom home with a mold issue, a 3,000 sf 4 bedroom with no problems is probably not a good comparable.
The next question you need to address, especially in our current market, is what were the conditions of the sale? A seller on the brink of foreclosure might take an offer that a homeowner who is in good shape with his mortgage would refuse.
The final question is when did the comparable sale take place, and what has happened to the market in the meantime. What has happened to the market is influenced by national factors, such as interest rates and the availability of mortgage loans, as well as purely local factors, such as the number of homes on the market at any given time.
Your best bet would be to work with a Realtor who has experience working with sales comps, and who generally has access to better and more timely information than you can get.
Prudential New Jersey Properties
973-538-5555 x211 office
Just to expand a bit on what Gina said, these sites basically take the sold number and attach it to an address. Alot of times homes may only have one picture on line and a local realtor may have been in the home while it was listed and can tell you if it had updated kitchens and bathrooms, hardwood floors vs. carpeting, etc. The MLS site that we have access to is real time so a new listing is input we get access to it immediately. It may not hit sites like realtor.com or individual company websites for 24-48 hours. Also once a home is under contract it is off the MLS active site but might still be listed on other real estate sites, even years after its sold or expired.
I know everyone says they don't want to be harassed by realtors, but the best, most accurate up to date information is through a realtor. If you really want just information let them know that up front and if you like the way they treat you maybe in the future you'd be inclined to call them to sell or help you purchase a home. That is how I look at it. I am in the information providing business even if i don't always get the listing or the buyer at least I am doing what I got into the profession to do help PEOPLE.
Lastly these real estate websites, as Gina mentioned, don't take into consideration outside factors that caused a house to sell higher or lower then other homes in the area and then they add some pre-determined calculation to determine your house value based on the info you provide. For example I recently sold a 2 family home for close to $400k when all the other homes in the area were selling in the $350,000 range. The reason it sold for so much was that i had a buyer who wanted to stay within walking distance to his mother's house. No real estate website knows that, so our knowledge can be extremely valuable as well.
Maybe a home is located near a gentleman's bar that would reduce the value but a website probably doesn't take that into consideration.
Well, good luck in your information gathering. If you have any questions feel free to call I don't mind if you pick my brain.
Re/Max Home Connection
I know your question was probably geared towards Trulia but honestly the best source of information on updated comps for your home and for homes that you are interested in buying is using a local real estate agent. Although Trulia gets their information from direct feeds and public information, real estate agents have this info at our fingertips. As soon as a how goes under contract or is sold, we have the info immediately through the multiple listing service. Using tax records we can track private sales such as for sale by owners too. I would recommend contacting a few agents in your area if you want the most up to date information for comps. Local agents also are familiar with each property and have a better understanding of what a house sold for and why unlike public sites which just compile that data of all homes in the area.
I hope that makes sense and good luck to you.