I don't use this strategy myself, but I'm interested in how those who do hedge against these dangers.  

Clearly claiming the power to reshape the rules that govern reality (economic & otherwise) is highly dangerous and can only be entrusted in your “highly capable” hands.

While going into the fall/winter months landlords need to be competitive with fewer tenants moving during these seasons.  

@Joseph M. 100% agreed and being a 'small' landlord in LA for a few years now, I  got to learn very soon how dangerous it is when your business is depended on 'tenant mercy' .... because it is just a matter of them doing a little research online or meet with their free attorney (paid with taxpayer money) and they are confident they can stay 3 months  free-of-rent and cause their landlord so much trouble he will pay them thousands and thousands dollars just to have this all go away... and many agree to seal their eviction records too..so now there are thousands of prior evicted tenants whose records are sealed , they are familiar with the process and know how to work the system!

At the higher end there are a lot fewer buyers.

There are many financial advantages to owning multiple leveraged properties over owning fewer paid off properties.

Mine has far fewer pieces, but it's still going to be complex to take over when I'm not here to ask questions too. 

Picking 20% out of the air would be dangerous.

Easier to rent, per sq ft better price, and I have fewer people living in my units!  

A self managed portfolio will likely have fewer costs due to more efficient addressing of maintenance and repair issues.