You really are not much of an economist, are you ? How does such an oversimplifying way to look at economic choice even go together with your ability to solve abstract mathematical problems?

Okay. To name just one objection to such an incredibly naive model of the market:

Misrepresentation of your actual valuation for strategic purposes.

Similar to the misrepresentation, "tactical voting", in voting theory: sometimes it is individually rational for an actor not to cast a vote according to his sincere preference.