You have to look at each situation. At a gas station, you are a draw for them. At a church you may want to offer them a "donation", it is very subjective to how much. For a bigbox they will most likely tell you. It is normal in a retail setting to at least offer the employees a discount (the owner you could feed free).

If the deal is free make sure you take care of however said -no problem!

My suggestion, start-off as if it's a partnership - of benefit to both parties, you will draw for them, they will draw for you. If they ask for payment ask what they consider fair, only you can determine if in your market that works.

PS: Churches have an advantage in that if your product is good, they usually have a few events every year and you would be the obvious choice to supply vending.