I didn’t know the meaning of jika (market price) and was charged a lot of money.

Jika refers to the current price for a product whose price changes all of the time. For example, a sushi restaurant will purchase that day’s fish at a certain price, which will determine what they charge for the sushi. Apparently, when the weather is bad and that day’s catch is low, the price of the fish goes up. If the price is listed as “market price,” you should ask what that price is before you place an order. Also, when you see the bill, if you have a question about it, ask for an explanation of why you are being charged that amount.