I'm in NSW Australia so my legal obligations may be different to yours.
I'm in the processes of setting up to sell soft and alcoholic drinks to guests. A few cans of soft drinks and a few cans or bottles of beer. Perhaps a bottle or two of wine, maybe something local. Legislation in NSW makes this easy and cheap (basically free) as long as the accommodation holds 8 or less adults and the alcohol is purchased from a retail store (no selling home-brew), and I have a Responsible Serving of Alcohol certificate. (Note: not an exhaustive list of requirements.)
Issues regarding potential access to alcohol by minors are avoided because the host is responsible while at the accommodation, and they must be over 18 to book.
My plan is to have a small bar fridge clearly marked DRINKS NOT FREE or words to that effect, and make the service terms clear in the listing too. Payment by a cash tin, or through Airbnb somehow (still sorting this out). The big fridge in the kitchen has filtered water and an icemaker so the guests already have access to free, unlimited cool drinks so I don't feel bad charging them for the convenience of buying something they'd normally have to get from a store.
Has anybody else done this? Hints and tips (including "Don't!") are appreciated.
An interesting fact: in NSW hair salons may provide patrons alcoholic beverages without any license.