The more reliable estimate is given more weight in the valuation. A purely statistical AVM often includes comps on a grid as that is what their lender clients are used to seeing, even if those comps are not used to estimate the value. Users typically set a cut-off for acceptance or rejection of a value. No AVM is perfect. They all have data problems.
Some models perform better than others, but all depend on data to get reliable results.
If you're trying to run an AVM in an area with few sales, it won't be very reliable. If the AVM database has no property characteristics for the subject property, it won't run if it doesn't allow user input. If you're running an AVM from a vendor that also provides better data than another equivalent AVM, it will be more reliable. He has been working on the database for three years. It covers 57 counties in New York, excluding the city of New York and Nassau and Suffolk counties.