Not all answers are conducive to such subtle manipulation, though. If the user asks for an algorithm to solve the knapsack problem, it's kind of hard to stealthily go "now let's see how many Coca Colas will fit in the knapsack". If the user asks for a cyberpunk story, "the decker prepared his Microsoft Cyberdeck" would sound off, too.

Biasing actual buying advice would be feasible, but it would have to be handled very carefully to not be too obvious.