It all comes down to Costs... but keep in mind that a full roof replacement, should give you a new Warranty on it, and extended lifetime and lower insurance costs too!

We use delta fixtures as they have warranty a couple times even when it wasn’t thier fault.

Is there a way that sellers should validate this information?

Tax deeds are given without warranty or covenant of any type; it is the purchaser’s responsibility to determine what, if any, interest in the property is actually being purchased.

I think your points are all valid and you're definitely more savvy than me lol.

In light of the fact that the leases are a scam I would not feel guilty but would still try to prove the leases are not valid first. 

This is a valid example of an industry that was eventually exposed as being vulnerable to fraud, and once it was exposed, people were like..."

If it's because the neighbors are making valid complaints, maybe do something. 

Of course, the virtual numbers that the tool spits out have to be validated "the old fashioned way" by confirming the assumptions the tool is making (comps for daily rental, occupancy, vacancy rate, seasonality, etc.) 

What comparable rentals have you looked at YOURSELF to validate how much rents are going for in the area, so YOU know what you can raise them to?