I run a coffee vending machine (which means you put in money and a cup with water sugar and coffee granuals come out mixed together) in a yeshiva. if you learn in the yeshiva you press certain buttons and you get a free coffee; if you do not learn in the yeshiva you have to put in money and press other buttons to get a coffee and there is a sign on the machine saying that.
Someone not learning in the yeshiva came and was playing with the buttons and pushed the button for a free coffee (which is very likely to happen) and came to me and said that by mistake a coffee came out. and wants to give me the ready made coffee. I have no use of that coffee. Does he have to pay me for what I charge others, or only the cost of the individual ingredients?
It appears that he has to pay the value of the ingredients, and not the full value of a cup of coffee.
The person in question “took” a cup of coffee by mistake. His status appears to be that of a gazlan be-shogeg, an inadvertent thief, which involves a dispute among Poskim (see Machaneh Efraim, Gezeilah 7; Shach 348:6; Ketzos 25:1).
Based on the opinion that an inadvertent thief is not considered a gazlan, it follows that the coffee never actually “entered his property,” so that he won’t be liable to pay the full value. Instead, he will have to pay the value of the ingredients alone, provided this is more than a perutah.