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).

When you list a retail house, you are going to aim toward higher comps to push your listing price to wherever the market can handle it, (although I make damn sure my sellers are aware of the most accurate and TRUE comps that exist because the appraiser sure isn't going to care to pick the "better" ones) and when your a retail buyer's agent, you find the comps that support those lower prices you hope to negotiate down to.

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 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).

Most contractors worth a damn are already booked solid for the next two months.

What else should I consider and pay attention to”Im just slowly noticing how some people on here will basically restate your post and say, “damn you messed up, good luck next time!”.