How to calculate rehab cost without inspection?

[Vee Vu]

Hi everyone. Quick question: How should we decide rehab cost without inspecting the house? 

The house is in Gardena, CA and there are tenants living in. Therefore I can't come and take a look. There are 2 beds, 1 bath, 963 sqft and 7400 sqft lot size. I know we can always inspect the house during the due diligence period, but I still need the rehab cost estimation to calculate the MAO (maximum allowable offer). Thanks!