Residential properties can be bid up by irrational exuberance and as long as the comps support it the banks will loan on it. A commercial property is a business appraised by its income.

What's hilarious is to look at an appraisal of a three family for example, the dishonest appraisers will torture the numbers so that the three completely different methods of appraisal: comps, rents & replacement, all fall within a couple of percentage points of each other.