Bypassing demo permit application

I have a contractor buddy who builds roughly 5 residential homes per year in Toronto and York Region. During the course of one of our conversations he had mentioned that you don't need a permit for demolition. However, from what I understand you need to apply for one.

What is he doing, what is this grey area? Do you need a demo permit for a large reno (70% or less of the house).

I'm just trying to get all the numbers on paper so I can figure out whether is it realistic for me to buy, repair, flip at this moment. Or if I have to budget way more. If a demo permit is 3-4 grand, I'd want to find a way to save it.

Have you guys any background about this? Is there a fine if you demo without a permit, would it be cheaper to just pay the fine?