Estimating rehab cost prior to tax deed sale

[Casey Barry]

I'm a new tax deed investor. As a tax deed investors we bid on properties without having the chance of fully walking the property. What is the best method for estimating the rehab cost of a property without seeing the inside. Most properties at the tax sale are occupied or you just can’t get access other than driving by or looking through a window if you are lucky. Knowing what a property may cost to rehab will directly affect what I am willing purchase the property for. Any advise? Please advise.