I think you can get them to fix items that they didn't do up front correctly if that is the case, but any negotiation is going to be before you go under contract otherwise. 

Hey guys,I've been working on a flip for a while and we're almost done with the project with only final items remaining.

But there is that item #2!!!

These items were in the lease. 

Additionally, charitable donations might offer a tax deduction if you itemize.

HVAC, roofing, foundation, plumbing, electrical are all mechanical items which would sway a deal. 

The real work does come in with driving around like you mentioned, maybe being creative and showing properties they may not have thought of, and articulating different ways to offer on a property, just to name a few items.

what kind of shape are the big and medium-ticket items in - roof, mechanicals, appliances? 

If they attend the inspection, they can only object to items that they object to at the inspection or that the landlord adds later if it is not noticed at the inspection.  

I actually wrote down all the appliances and capex items and amortized it based on the projected life expectancy and it all comes to just over 15%!