Estimating value add rehab prior to loi

[Hassan O.]

What do you use to estimate rehab cost for your underwriting in the initial analysis of a value add opportunity Prior to making an offer? Is the broker or sellers estimate what you go on or are there loose rules of thumb you follow?For instance you have a 100 unit opportunity and the broker / seller claims 50% of units have been rehabbed over the past two years with the rest ten years ago. How does a person resolve this with knowing the conditions of the others?