Property values have gone up approximately 40% in the last two years.

I responded to her FSBO ad and made my offer which she happily accepted: a 36 month lease option; I'll bring her mortgage current, (1 month, $800), and continue making the monthly payments; option to purchase price of $88K, (my estimate of value, $100K); and I had the right to buy, sell, sublet, or assign the property at any time during the 36 months.

Recommend you have your Engineer do cost estimates. 

"Within approximately 30 days, you will be emailed the first of two "Post Closing Documentation".

Here are the numbers, so you can see what I mean.The numbers are the following: 359,900.00 sales price (purchased Dec 2015) 89,975.00 down payment (25%) 10,000.00 closing cost (estimate - I don’t remember the exact figure) 7,000.00 required rehab (estimate - I don’t remember the exact figure) 106,975.00 Cash invested 3,900.00 Rental Income (actual figures) 150.00 Parking Income (actual figures) 4,050.00 Total Inflows (400.00) Utilities (250.00) repair budget (not an actual outflow, yet) (2,200.00) Mortgage (Includes insurance, taxes, and P&I) 1,200.00 Operating Inflows 14,400.00 Yearly inflow 13.46% ROI If I were to use the 50% rule I would have discarded the property. 

That did, if you have an AirDNA subscription, you cab look at the comps underlying the estimate.

That will give you a good baseline to start from.You can also use AirDNA by buying the specific area to drill down farther.Try https://www.awning.com/airbnb-estimator as well.

Under each state that I’ve dug into the laws, the final investor should not be able to do their own estimates because they can’t be shown the house… again acting as a realtor under a “net contract.”

Do You have experience in construction, rehab, repair estimation?  

ROE shows the estimated returns forthe next year.The condos are in the same complex that I purchased for $195,000 and $207,000 in 2020with a 25% down payment.