How do you calculate rehab cost given you can’t look inside? 

This is the form any lender should use to calculate you income (ignore the branding, it is the same for every lender):   https://www.biggerpockets.com/forums/49/topics/1224525-fha-l...You will see what you can add back from your 1120 based on the % of your ownership. 

Quote from @Robert Quiroz: Quote from @Rick Albert: You have to keep in mind there is a calculation when it comes to increasing rents.On my last tenants of three years, I only increased once.

I tried using the biggerpockets rental calculator this morning and the cashflow was negative, but I may have been too conservative with the numbers.

Head over to bank rate or and take a look at the mortgage calculators, plug in the numbers and get an idea of what the property needs to generate to satisfy the intended debt.You still have to underwrite the deal for the non-finance expenses as well(typically 40-50% of the gross rents). 

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

I've been running the numbers on different properties using a variety of online calculators for properties that I initially thought looked like there may be potential.

You'll just have to figure out how much utilities normally are for your calculations. 

Usually my agent is the one asking me to how to calculate ARV and find cost to fix the bathroom,etc.

Hey Robert,I recommend looking at BiggerPockets calculator.