Garage conversion permit

[Johnny Sooc]

Hey all,

I'm looking at a SFH that is on sale in my area. The listing agent said the garage was converted to a living area before the current owner bought it. It has central heating/AC, insulation, a half bath and closet. They didn't have a permit for the conversion.
My plan for this house is to buy it as a primary residence for year. Rent out the garage on Airbnb while I live there. 
Once I move out I will rent it by the room.

The unpermitted garage poses a lot of risks. I want to try to get a permit for it after buying it.

Has anyone bought a house with unpermited renovations then try to get a permit after? Any success?