As already mentioned, the most accurate data will come from a licensed Realtor. We have the most up to date information on what has sold, for how much, and if there were any seller concessions. In addition, in a market like we have today, the properties that have just gone under contract are a more important indication of market value. This is because the market is still shifting, in some instances weekly. Because it takes, typically, 45 or more days for a property to go from an accepted offer to actually closing, closed sales data represents the market 45+ days ago.
As a buyer, the professional services of a trained realtor cost you nothing. The seller nearly always pays the commission, so there is no reason not to enlist the expertise of a realtor
If you need validation of the value of having an agent, you can get that and more answers to many another question you may have from the HUD Web site: