If your ARV is 215,000 the 70% number is 150,000 and then subtract repairs off of that.  

We insure a few hundred homes at anyone time and have a Proctor account.. its like a zuriich.. and so we can add one day and subtract one day and we pay a monthly rate.. so on some of these cheaper mid west homes we may pay 20 to 30 a month but if the property is off the books in 90 days its only 90 bucks.. and they bill once a month in a rears.. though with that we have a 5k deductible.. which hurts on wind/hail damage for roof replacements.. and it takes for ever to get a claim through they will come through but you need to have the money to do the fix up while the claim is being processed.

And then for salary, it probably has to be a check like we get from corporate America jobs (with Medicare taxes +social security taxes subtracted,  etc?)

This is subtracted from the the net sale and that is your gain.And the gain is made of two components - gain and depreciation.

This would mean a total of $56K you would be on the hook for if you just bought the house without knowing this (if it’s even possible to buy a house without a titling company, honestly, I do not know).A title company will discover this information, and at the closing table they will subtract the $56K from the proceeds the seller will receive, put this money in an escrow account and order payoffs for all of the seller’s debts against the property.

From there I  can subtract the material cost and find out what kind of margin they are working with .Some other things to consider, larger companies will have larger overhead.

In general, the two SFH will appreciate more than the duplex even after you subtract the "cost of two roofs" that you have to replace only once every 25-30 years. 

.$2,875 Rents x 12 = $34,500 Incomeminus (Taxes Insurance Maintenance Vacancy PM)- $5,500 - $1,200 - $4,800 ($100 per door per mo) - $3,450 (10% vac) - $3,450 (10% PM)= $16,100 Net Incomenow you just need to subtract your (Mortgage x 12 months) to see what's leftoverassume $200k purchase price, 40% down, 5% 30-year = $644.19 x 12 = $7,730.28or about $697.48 cashflow per month

For starters, it would be wise to include a month of vacancy (subtract from 8.3% from expected monthly rent). 

Then you work backwards subtracting your costs and profit to get it to get to an as is value. .