You can also earn very competitive interest on crypto, which I'm experimenting with now (8.6% APY on USDC, for example).While this is still early, and there are some logistics to work out, I'm sure any real estate investor will understand how disruptive this truly is. 

Buyers can go on zillow, trulia, or any countless other site and know true values and be more educated than the broker.This is what happens when there is market disruption.  

And sure, maybe he is a complainer, but if he's not able to live his life without constant disruption then you're likely going to have the same issue in the future with anyone else that lives downstairs. 

It's another to disrupt every weekend day, ever weekend for 3 weekends. 

If the unit is occupied and we need to disrupt the tenant to show it, we require a partial pre-screen.  

It didn't disrupt my business, it didn't cost me any more other than a bit more time which I took from my non-productive time.

The reality is that reducing income to "potentially" save costs does not save costs it only reduces the return on the property.Once you graduate from a couple of doors to tens or hundreds a stricter business approach is necessary to insure maximum return, Vacancies are built into the expenses and the percentage of tenants leaving over a rent increase is very rare as professional landlords quickly learn.Landlords are simply justifying their suplimenting of tenants rent out of a illogical fear that tenants will decide to disrupt their personal lives over having to pay market rent.

Or their kids were completely out of control running through the building and up and down the stairs without the parents controlling them, and I was sure they would be too disruptive to the other tenants.  

OP did not mention this person causing disruptions or complaints from neighbors.

Tenants don't like to have their lives disrupted by maintenance people, so they tend to not report problems.