You have a basis for judgment. Whether they buy it or not, they will feel that the price is too high, and if they buy, they'll not be as happy with the price they pay as they otherwise would have. That's why it is often smarter to ADD value to a product as part of a promotional deal, rather than just cut its price. Numerous studies show that consumers use a brand name as a substitute for product quality. This is especially true when it is hard for the buyer to quickly and independently evaluate the quality of the product.
Common sense is a huge hurdle for a seller to try to overcome.
One of the great challenges Starbucks faced was to get people who were used to paying a dollar for coffee to spend three or four times that amount. Second, most buyers will take your word that the quality of both items is equivalent. Buyers are generally trusting people. If you tell them an item is on sale, they'll believe the price they see is lower than the one last week. In general, buyers will believe that an item on sale is a better value than one which is not.