Is my informing customers that the gallery owner has increased the price of an item beyond its original price considered a sin and a betrayal of trust?

It is permissible to sell a commodity at slightly varying prices, especially if the seller increases the price in anticipation of the buyer's bargaining. It is not permissible for you to inform the buyer that the store owner increased the price for bargaining, as this is a disclosure of a business secret that you were entrusted with, and it may lead to the harm of a lack of trust in the seller's prices.