I work for one of the major players in lending, and when we hire valuers to go out and value properties for us, they take a look at the property the market and what risks there is of the property price decreasing, along with how it compares to similar properties in the area.

Yes there have been some instances when the clients havent agreed with the valuation and it is for the very reason that someone else mentioned earlier, if there are no sales in that area to compare to what has a valuer got to work with. Though 99% of valuations i request would come back with the agreed purchase price as the actual valuation amount. Unless someone seems to be getting a bargin do i tend to see a higher valuation.