It's not something I would try. There is too much opportunity to lose money from people taking snacks and not paying for them. I work for a company where people sometimes put fund-raising candy in the lounge with a sign asking buyers to leave their contribution in an envelope. Generally, at least some items are taken without payment.
We have one at work. It is being taken away because too many people take food without paying. I don't think its a good idea, a regular vending machine is better, in my opinion.
Depending on the area of where the vending is to be in, you have to have a good faith in the local residents. A heavy populated area can be a danger zone, victim to a break in can cause the business to loose a lot of money. If the business is a big profit business then don't attempt!