I have done several hundred rehabs and been in the construction and real estate business my entire life as someone else noted always add the osf ( oh sh*t factor) to every estimate I use 20% when I started and still do today.  

@Larry T.

This will also help get them psychologically fully committed to it. 

@Larry T My logic using the 50% rule is: $1200 per month rent - 50% = $600 per month gross income - $200 interest portion of mortgage payment leaves me $300 net income and $100 principle.

@David T. 

Unless, there's a large code violation, that I'm trying to get a total for, if I think I can negotiate out a huge discount, before committing to the deal.

Once you find a good fit, a lender who tells you yes more than no, then you can commit to a long term relationship.

I agree with Jesse T. 

Originally posted by @Kimberly T.

Great point @Jesse T.