It really sounds like you are not experienced at Commercial Property:
Assuming that you were keeping whatever business/tenants that are in there; the Seller is inlikely to share his personal/business finances with a stranger. You will have to show them that you have integrity and are a serious Buyer, before they will share with you.
If you are going to change anything; then the previous income statement will be meaningless to your situation.
In either case, you obviously will need a good commercial Realtor helping you.