Zillow is a fine place to start, but shouldn't be the only source of data.

@Prithvi SriCommercial is very relationship-driven.

Far from a perfect science but the more data the better!

A local private lender that is asset driven is likely your best shot.

But the methodology works for 3 or 4 units too. 

Check out Awning.com's AirBNB estimator - https://www.awning.com/airbnb-estimatorIt is free and can augment your data. 

Do some data-based analysis to determine if this investment makes sense as opposed to emotion driven decision making.

We manage about 350 units of multi-family apartments in Norfolk, VA and are constantly measuring data/market trends as it relates to leasing, PM churn, and growth in the area. 

One thing that would be helpful to investors from the professionals is hard data, the statement numbers don't lie, carries weight as long as we do not make them lie.

If there's a hole, it may be a red flag.b) sensitivity analysis: I examine all the assumptions, and make sure I can live with the worst case scenarios.c) "Stall and see": if they are getting money over multiple years, and there is no penalty for investing later, I would usually wait so I get some real performance data, versus having to look at theoretical pro forma information.d) Recession stress test: I will not invest in anything, until I subject it to recession level stress and see if I can live with the result.