True "straight line" depreciation is not the norm over say a 70 year total life, with most depreciation coming in the last few years. But over a short haul (5-10 years) graphed on paper the line is basically "straight" and we are talking about adjustments which should be within a few years apart.
I would question the judgment of using a comparable with more than 5 years difference in effective age, because it suggests an adjustment that is quite large.
In explaining "average", it is a judgment call just like "condition". But, as I recall, the instructor suggests average means the exterior is maintained, the appliances function, and interior items are replaced as needed, etc. whereas above average may imply serious remodel of bath or kitchen, extensive remodel (like whole house carpet or appliances prior to the normal life of same) even to the point of excess. Below average maintenance would suggest things like not fixing broken items. Extreme worn or soiled carpets not being replaced, broken windows, damaged doors, walls, flaking paint, etc. In other words, functional items needed to be fixed.
The value of a property would be independent of its occupant - and reporting otherwise would likely violate federal discrimination laws. As for Hell's Angels. The average HA is about 50 years old, and many are well over 60. They have become pretty mainstream in the Biker world, perhaps a little more liberal than average folk on drugs and booze. Last week, they were in Gunnison, CO. The Gunnison police made only one or two arrests for public intoxication, otherwise pretty much average bunch of conventioneers having a good time in the Rockies. I doubt they make that bad of renters, though you might have to hire a rival gang member to evict them and hope there is a house left afterwards!!
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