I manage around 400 rentals and probably terminate a couple dozen every year for lease violations.

Neighborhoods can change in a couple blocks. 

When you own a couple of units, the odds of there being unexpected vacancies that overlap each other are usually low, but when you acquire more and more real estate, the odds of tenants moving out around similar times increases. 

Quote from @Brittany Minocchi: I'm a bit farther north, but I've helped a couple of people with loans in that area - the properties seem to be working out well for them!  

A couple of questions about determining the ratio of units to population.   

I was a Moderator for a couple of those years as well. 

If I own a property with a 1k mortgage per month and it stays empty (or I'm trying to evict) for a couple of months then I'll be ok.

A couple of caveats though:*I've been doing this for 5+ years.

As a couple others said emergency would negate the $500 threshold but they should contact you to notify when it happens.

It's a winning combination of direct access to industry experts coupled with building lasting relationships and get direct feedback on your strategies in small-group format.