Earlier quoted context omitted.
Let's say you grab a can of Coke in the grocery store, shelf sticker says 49c. When you pass on the cash register, it clearly shows $5k in the cashier's monitor, and the point of sales screen, so you're charged $5k. Ooops, says the grocery store: Coca-cola raised the prices, not me.
Have you used amazon subscribe and save? What you described is basically how it works. You're agreeing to auto-buy at whatever price amazon sets on that day. The only exception when you first set up a subscription, in which case the first delivery's price is locked in.
The price will fluctuate, but this is on another level, and deceptive since they had already stated what the price would be.