They are a constant liability, both in decades of monthly payments as well as impacting your debt-to-income ratio.

We have found that reducing rent doesn't usually impact the length of the stay.  

Making mailings is one way to find good deals, but the return on a mailing is very low and expensive.Doing a mailing campaign is a passive way to market for deals - If you want to accelerate your potential to make money in this business, I would suggest using active marketing ---Farming - looking for vacant, ugly houses - tracking down the sellers - make an offerSit in your local rent and housing court - no body wants to be there - great place to find burned out landlords who will be glad to discount their property to youExpired listing - these are sellers who have a property that did not sell - you can make their dream of selling a realality and profit at the same timeRather than licking stamps, designing silly yellow letters or post cards, stuffing envelops, buying postage, running to the post office or sitting home waiting for the phone to ring -- you'd be lot more successful by entering your market and doing peo-active marketing for the gold nuggets you are seeking.

Too soon to tell what impact, if any, the new casinos will have, but worth paying attention to.  

Plenty of high density housing ideas look groovy until you look at second order (parking) and third order (traffic) impacts.

But I also look at listing comps (the competition and/or what's not selling if high days on market), foreclosure comps (any foreclosures nearby that could have an impact), and neighbor comps (is this property overbuilt or underbuilt for the area).3.

Furthermore, being cash flow negative is going to severely impact your DTI and thus your ability to purchase other properties.

Location can have a huge impact.

@Austin Whitcomb the question about student rentals being impacted by online learning is a good one.

I would be concerned about how sec 8 compliance might impact your bottom line in the long term.