The plaintiff would like you to think of this case as picking a pack of gum up from the store shelf, getting to the register, and being asked for more money than the posted sign.
I think of this more as showing the clerk at the register the list of what you want to buy, including an auto-generated price estimate, and the clerk goes in the back and checks and says they’re all out of the limited inventory of discounted product but they’re still willing to sell it to you at regular price.