See if he will share the financials with you and go over how everything breaks down so you can see where all the money goes. Do you have the money to buy the business outright? If not, can you get a loan, will you need investors, will he do owner carry? This is important to consider because while the business may be cashflowing, does it currently cashflow enough to cover the current expenses plus whatever your financing will cost you?

Would you be willing to split ownership with potential investors if you can find them?