As far as the seller determining the price, that’s true but the price they set is set on the basis that they aren’t lying about what they are selling you.
If someone sells you a pure gold box that turns out to just be aluminum wrapped in gold foil, that’s fraud even if you agreed to pay for the pure gold box. The seller did not provide the thing you agreed to pay for. It’s the same in this case, the seller allegedly lied about what they were selling to get HP to agree to an inflated price.