Is inheriting tenants always a bad idea for SFRs?

[Mitchell Go]

Is buying SFRs with tenants in place always a bad idea?

I'm currently focusing on SFRs and I was thinking of buying currently tenanted rentals paying below market rents in B- neighborhoods. I'm thinking if current tenants are paying slightly lower than market, I could negotiate down the price but still cash flow to cover my expenses. 

Before you even buy the property, how do you do your due diligence? 

Are rent-ready costs typically more or less expensive? 

How does this work if you want to switch to a different property manager? 

What are the typical issues that you've encountered and how do you avoid it? 

Any experiences and thoughts would be much appreciated!

Mitch