Work with the IRR calculations to compare your property with negative cash flow versus a property you can find with positive cash flow.

They can use the recent sale of one for $650k to value that property BUT they are also updating the value of the other property that did NOT sell and using comparable sales or other more general market appreciation statistics to do it. 

Could be local market statistics, information on grants for 1st time buyers locally, etc etc...

You can probably find statistics showing where climate related risks to property are likely to increase.

Check airDNA and get statistics. 

Not because they suddenly love their house again, but because the path to a workable deal broke down.Layer on the fact that foreclosures are climbing, and the picture sharpens.These aren’t abstract statistics.

I'm interested in fix & flip and rentals, and have some experience with both, though not a ton and not in New York I'd love to chat with investor-focused lenders, investors, Realtors, contractors, people familiar with buying foreclosures, and people who know the areas.I really do try to do my own research but all the statistics and comps in the world don't tell the whole story and I'd love some insight from locals!

-The single-family median price was statistically flat at $335,000.

This deal will still have negative cash flow in year 30 when I pay off mortgage. 

To address negative cashflow, you could MTR or STR bedrooms in owner-occupied unit, maybe even in the other unit.