Banks are looking for either your ability to make payments, or in the case of income producing properties, then they want to see that the property can make the payments. Although, they will often discount the current rents to something like 60-80% of net to account for unexpected issues in income. Do not, under any circumstances, go buy rent producing property without representation from someone who has a boat load of experience buying these types of properties. It is a science that is learned through experience.
You should also have an accountant or financial planner that knows how to pour over the income/expense history. You'll need a very good inspector as well.
Tread carefully, what looks good to you might not look so good after the experts have given it a once over.