Can you trust Zillow Zestimates? If not, how to estimate value?

[Aaron Blevins]

Was talking to a lender friend earlier who said Zillow Zestimates aren't trustworthy at all as they don't factor in REO sales.

So aside from performing an actual appraisal or BPO, what are some good rules of thumb for estimating the true value of a property? 

I'm looking at rental properties inside the city limits of Columbus, Ohio in the Zestimate range of 50-80k, but listed for sale far below that, and I'm curious what values would actually come out in an appraisal.