When I was an apartment broker, I always made sure and give prospects 3 years of operating history....unless there was something to hide! :)
That said, with the market having so many buyers and so few sellers, today, I often don't see anything other than a pro-forma. Depends on the broker. Residential agents selling a 2-20-family are usually too unfamiliar to even provide RENTS in their listings, let alone actuals for 3 years! And they always leave off property management. Commercial agents should have no problem giving you what they have. But if they have a ton of interest, and the other interested parties aren't asking for actuals, you might find yourself getting beat to making an offer.
Personally, I don't care if I have the financials prior to making an offer. Why? Because I will probably use my own numbers anyway. Expenses are usually lower for the seller than I expect, and vacancy is usually higher than I forecast. For example, property taxes will go up, I will pay a manager for EVERY property, insurance can be estimated with a quick call to one's broker, and utility bills can be had by calling the utility providers. I almost always figure expenses at 40-45% of ASKING rents (rent roll)...if I see numbers much lower than that, I'm suspect.