Put a contingency in to have it inspected just before closing AFTER the water has been turned on and ensure those costs are paid by the seller along with any outstanding bills. 

When I buy I send a FOIA (Freedom Of Information Request) request to the city to confirm zoning, violations, outstanding fines, outstanding water bills, etc.  

Tenants even have a management portal where they can see their payment history, outstanding balances, and open maintenance requests (while uploading pictures to support).

Outstanding!

So generalizing with data from the sites you mentioned doesn't account for performance based on an outstanding property from an average one....think of a 'zestimate'..it doesn't know the house was just remodeled and is superior to the neighbor, it is just taking averages of the area. 

If you were to have negative cashflow or a loss, that gets subtracted from your taxable income from your full time job for example and then they ask for 30% of that new lower total.This would be good for a rough calculation, so you know not to spend the entire amount of the proceeds so you have them to pay when you prepare your tax return and pay your outstanding taxes.

I'm looking to do a brrrr and will be buying a property with a lot of maintenance outstanding.

You could spend more time fishing and with the proceeds buy a bigger boat, and with the proceeds from the bigger boat you could buy several boats until eventually you would have a whole fleet of fishing boats.

You can look up the original mortgage value in the public records and use an amortisation table to estimate how much is outstanding (you´ll know the exact amount when a judgement follows the lis pendens).

If its to refinance after the project is complete you want to cashout upto 75% and pay back the loans outstanding .