The “ Limit — three per customer” signs are there to encourage people to buy 3. It makes the items seem like more of a bargain.
The free market does not stop the Red Cross for sending in tanker trucks of free water.
The free market solves many more problems than it causes. In this case, there is nothing stopping people from buying from the stores 3 cases at a time and selling them on the street for a buck or two or four per bottle. People are already doing that when there is no shortage. The store owner that charges $99 per case has to decide if he is willing to risk permanently losing customers. The free market does not fix the immediate problem (nor does your “solution”) but at $99 or per case the supply will quickly increase and prices will quickly drop back to normal. Stores like Best Buy get accused of price gouging for selling cases of 42 bottles of water for $42 when their normal price is $1 per bottle.