Is it reliable to pay insurance, rent a car and deliver food in Shenzhen?

Not reliable. If you want to deliver fresh food in big cities, there are basically professional companies to do it. If you rent a car and then deliver food, it is not very reliable in itself. First of all, find the source of goods, and secondly, rent a car, which may make ends meet. If you want to try distribution, you can join some big distribution companies.