Everything that I've ran the numbers on a flip on has been extremely close margins, while looking to rent a property nothing is reasonable (ex. ive seen rent ~.5%-~1% of the purchase price).

What I do know is basically look at what needs to be replaced (EX: windows, interior paint, flooring, HVAC, roof, etc.) and then 'guestimate' a rough cost for each item.

I agree with you in certain markets that don't appreciate the returns are only what you can make on cash flow over a long period of time and you never have to sell or recapture deprecation or have major cap ex either of those will kill your returns back to next to zero.but you take high appreciating markets and these charts are not accurate at all. its the dead an dying or non appreciating markets that weigh down the US averages.. any property bought in say SF or SF peninsulas back in 08 have basically gone up 4X  and or more.. other areas say Detroit or other cities that saw mass movement out of area .. properties peaked in mid 90s and have been going down ever since .. with the exception of the craze to buy SFRs as rentals by out of country or state investors this has propped up values in these areas.. 

She wants to sell the land as her ex husband has passed away.

Are rental applications (ex.

The seller is the wife who cannot get her ex-husband in to sign off on the deed.

Keep in mInd that maintainence, cap ex and the other costs of owning the property still come out of your pocket as you live there

Ex. 

The City of Charleston will not allow AirBnB rentals to anyone who is not an owner/occupant and even with this the ordinance is very restrictive (ex., 4 adult max). 

Ex. we looked at a property last week that needed $110K (conservative) in rehab, ARV at around $525k.