By the Bais Hora'ah
Many hotels have drinks available for purchase in the refrigerator in each room. However, they charge more than double what the same drinks cost when purchased from a store.
Q 1: Is there a violation of onaah (exploiting the ignorance of the other party in the context of a sale) when they charge double the going price for the drinks?
Q 2: If someone wants a bottle of water but does not want to pay such an inflated amount, is it permitted to take a bottle of water and replace it with another bottle of water that he will purchase for the regular price?
A: Regarding the question of onaah, Halachah recognizes that there are different markets and the same item may be sold for different prices in different markets. Different types of stores are considered different markets and may charge different amounts. The same sweater will be sold for one amount in a clothing store and for a different amount in a department store (see Sefer Hilchos Mishpat, Intro. ch. 4). Similarly, a hotel is a different market from a convenience store and the seemingly inflated price that they charge is within range for that market and thus there is no violation of onaah.
The second question is whether you may take a bottle of water and replace it with one that was purchased for less money. It is prohibited to steal with the intent to repay the owner (C.M. 348:1). Accordingly, since the hotel intends to make money by selling beverages and has determined that guests will be willing to pay the inflated amount due to the convenience of having cold drinks available in their rooms, it is clear that they would not permit you to take a bottle to drink and replace it with another one, since that prevents them from making their intended profit.
However, if one did not know this halachah and took a bottle of water and replaced it, he has fulfilled his obligation to repay the owner for what he stole (C.M. 354:5). Although one who damages property is not obligated to provide the owner with a new utensil to replace the one he broke, a thief is obligated to either replace the utensil that he stole or pay the owner the value of the stolen object (Shach 354:7, as opposed to Ramah, who requires a thief to pay his victim with money rather than replace the stolen object).
Consequently, although the one who drank the water benefited from the drink, as long as he can provide the victim with a replacement of the stolen object, he has fulfilled his obligation. Even though the hotel charges more for the bottle of water than the thief spent on replacing the stolen bottle, he fulfills his obligation as long as he gives them a replacement bottle of water, even though it costs him less.