The simple truth - as you pointed out - is that lowering the rent - by definition - devalues the property.

I cannot imagine hating my assets so much that I would allow a tenant to hire some idiot off the street to destroy them.And then reward the destruction of my property by devaluing it through rent reduction.

Again resale issue and you de-valued your property. 

As you know that would mean a devaluing of the property. 

I was under the impression that you could only back out related to stated contingencies, such as if an inspection found something that significantly devalued the property, etc.?

It is simply very poor business either way to mention nothing of how it devalues your property.

The reason is that more rental units devalues the building and each owned unit as a whole.

Obviously you are dealing with buying from a hobby landlord that has inadvertently backed themselves into a corner and seriously devalued their property.

There is recaptured depreciation (depreciation is the devaluation of the property over time) as well as capital gains (increase in the property from buy price to sale price).

Beyond small business owners, another casualty of this is the devalued work of those making $15-$18/hr.