I use my realtor, along with comparing recent sales on realtor.com, Zillow, telia, etc.... The more sources you use, the more accurate you'll tend to be
their numbers comparables were actually lower than Zillow, home values, etc...
Because an appraiser, comps, real estate agents, CMA, Zillow or any website you may choose, will only give you an idea of what it COULD sell for. They are literally just opinions. Any of these methods are not a defacto value of what the property will sell for. Just because an appraiser says it's worth $$$$$$, does not mean it will sell for that. It's only worth what someone is willing to offer to buy it for at the time.
Case in point, this property here, we sold back in September. We had offers from 150k to 175k, it appraised for 172k... We accepted an offer of 160k. Our investment group bought it for 50k, it was appraised at that time for 115k. Properties are only worth what someone is willing to pay for it.
Use any of the above methods to get an idea of what a property is approximately worth. We buy an sell a handful of houses everyone month, I frankly like to search around Zillow to see what comparable houses sold in the last 6 months in a few miles of the property in question, it's faster and cheaper that most other methods, as all you really need is a price range.
Appraisers and real estate agents Only use comparable sales.....with adjustments for condition, location, amenities, etc.......something Zillow and other websites can’t do.
Market value is determined by using comparable sales data of recently sold properties in similar condition, and neighborhood. Comparable sales data is the best signal as to what the market is doing. The reason buyers swear by MLS comps is because one of the most important signals in the determination of value is how recent those other sales were, and that data is usually only in the MLS. This is especially important in hot markets where values can be volatile and increase or decrease quickly.
Zillow and its counterparts usually only have access to public record data which is in most areas delayed past the point of usefully determining current market conditions.