Could you make a living off of owning a vending machine?

Of course you can

Lets say you sell cans of coke for $1 each, and you are paying 60c - that means you're earning 40c per can sold. You then have to weigh up the overall cost of ownership (restock-costs, insurance, etc) versus your income.

To make a living from vending machines - you would need a fairly large network of machines - and a minimum expectation of sales over a week (you'd be looking at footfall versus sales). Each machine would have unique costs associated with them, but you would know where to place it and where you are making the best income.

If we were to assume you wanted to make $400 per week - that would involve selling 1000 cans of soda per week. A single machine might be able to handle that (that works out at a 6 can per hr, average, BEFORE you add in your overheads - ground-rent, electricity, insurance, cleaning, restock & maintenance...etc)