With all du respect chefs, I realize the hurdles in today's economy to start a business and work for yourself. Trucks, trailers pop up tents, are much less than brick and mortar....in addition you can go to the customers. Yes, if there is already a donut guy at a farmers market they will probably not allow a second. So I agree, do your due diligence prior to embarking on the mini donut path. Unless you are doing it as a hobby and if is just for fun, do not spend money unless you are sure. I met a lot of nce people And bought the machine second hand and made a lot of donuts. Maybe it is the area, maybe it's the luck I guess I'll never know.
It is a lot of work to just keep the donuts flowing - I had people ask me if I could do malasasas, big donuts, fried fish, etc,I just say "sorry" only do donuts w cinnamon sugar, powdered sugar or plain. They smile, take a sample, then buy a bag.
Good luck with your donut truck endeavor and it's good to help someone else with knowledge if you can share experiences -