Have you observed them walk; if so, how is their gait pattern? 

Also, for moral compass type questions an in-person interview would be best so both the verbal and non-verbal communication can be observed.  

Showing: If the prospective tenants pass that stage, we invite them to see the property, at which time we observe and find out more about the prospective tenant.

Over that two years, I have observed they keep their aparments in bad condition, are very loud and bothersome.

Then observing and guiding tenants back to the terms of the rental agreement if they stray.

And sites like padmapper and zilpy, and zilliow and Craigslist help to do that survey; I bookmark the search for those so that when the time to increase comes along, I click the bookmarks and observe the competition in the market. 

@Brian SinghMy guess is SF price will be down 10%-15% by 2022, so I am on the sideline..That said, my observation from 2009-2011 is that by the time the market hits the bottom, the listings are all bad - bad locations, bad floor plan, bad whatever....So if you want a quality property (like me), you might have to get in sometime in 2021 before the market hits the bottom, and be willing to pay a bit more, knowing the price will drop more...

It's what I have observed ...

We observe.

I don't use a property manager so I cannot give feedback on one specific company over another, but based on my observations over the years there are a lot of student rentals that are poorly managed and in bad shape.