On other thing, if a bank loans you a million dollars using your outhouse as collateral, that is prima facie evidence that the value of the property at the time the bank loaned the money was at least a million dollars.
That makes sense. Then there are subjective things. One selling point we made for building a church building with denominational help was that a large shopping center was going in down the road, a plant was expanding, and builders were preparing to build more homes to accomodate more residents.
It was all true, but then a series of economic hits happened about 2008 to change all the above. Those things never transpired.
Same with any property, I imagine. It increases or decreases in value based on subjective projections for the area, none of which are dishonest, but that doesn't mean they can't change.