It is a modest use of my time and the expenditure is minor but I find it helps in building goodwill that comes in handy with subsequent issues as they arise.

(had newspaper ads to prove it) It was subsequently tax assessed at significantly more than what I paid for it (paid ask) and I contested it all the way to the state tax tribunal and lost.

While some of the suggestions above may pass muster on the federal side, your state fair housing laws may be much more restrictive.Here in MA, you had better treat everyone the same or there will be a smoking crater where your bank account used to be.We have state-employed "testers", who do things like apply for rentals.  

We then assessed their heating costs & subsequently upgraded the furnace to HiEff. 

Many courts are subsequently not keen on the idea of frivolous lawsuits, and often throw stuff out really fast for that very reason.

@John TeachoutFrom what I can tell, just the first one is free and subsequent listings cost - at least that's been my experience.

I have subsequently cashed out a few, but most of what I own is free and clear.

If it is cheaper to hold a unit vacant until the recovery, than lower rents and subsequently affect rent prices of all units, they will do that.

The additional money was from taking out a few personal loans ($20k, 32k, and 15k), taking 2, 0% cash advance offers on credit cards -and then getting a HELOC on the first property that we paid cash for to use for down payments on subsequent homes. 

If you only bought 50 or 60% LTV loans the market would have to really crater for you to lose money.Solution: c) Follow through with the foreclosure process and you end up owning the house.