Asking About Rental History?

[Aleksandrs Vilumsons]

When looking at multifamily properties, when is it appropriate to ask for rental history? When you make first contact? Do you wait until after you've walked through and inspected the property? I can get a pretty good idea of what rents should be and generally are in the area, but how would I confirm the current rents and rent histories for a specific property? I would like to know as early as possible if I would have to raise rents or continue at current rates so that I can have some sort of plan after the purchase is made. 

Thanks in advance