I think a monthly fee of $50-75 to use small machines would be a turnoff for busy tenants who likely are just looking for something to complain about.

It doesn't stop them from complaining about it...  

Says he complains about it to his LL.So I asked him how much rents he pays, and he tells me $700.00.

This way it controls how much they use.I like the idea of the mini split because otherwise they will complain if it is too hot/cold and someone has to suffer.

My experiences have been tenants complaining about everything  under the sun with a property just so they can get out of the $50-100 difference they pay out of the voucher.

The fact they are complaining online might be an indication the property manager dealt with them properly so be sure to ask the manager for their side of the story.I hope this basic guide helps.

If that fails to produce any results then you'll figure out real quick whether it's crummy service or crummy property.Investors complain about having to manage my managers. 

The funny thing is that the owner always told me that none of his other landlords make money and they all complain about losses... at the time I took it for candid and honest advice, but next time I will treat it as a major red flag.

This is especially true if there is mold caused by a leak upstairs or a unit on the other side of the wall.The close proximity of neighbors - When neighbors cause problems, your tenants will complain about noise, cigarette smoke seeping through their unit, etc.

These tenants have already started complaining about habitability, and have threatened dragging things out by requesting jury trial.