It's not as simple and straight-forward as a residential purchase. There are other things involved, more paperwork to do, and more time before it can usually close.
If you are going to be buying an Income Property and will be financing the purchase with a Mortgage then watch these videos. Each explains how you go about obtaining that mortgage, and what you will need to qualify. You might also want to know the maximum amount you can afford.
This video goes into the details about financing a larger commercial building, where you might need to have as much as a 50% downpayment to be approved for a mortgage