Some businesses use incentive schemes to draw in customers; I want to know about whether or not such schemes abuse human psychology or are otherwise immoral. Let me give an example. Imagine a sandwich shop that sells sandwiches for 2$ each; they decide to change the scheme, so that now, every time one buys four sandwiches, the fifth sandwich comes free of charge. To compensate, they raise the price of the sandwiches to 2,50$, meaning that either way, the customers end up paying 10$ for every five sandwiches. Yet people, especially newcomers to the shop unfamiliar with the old prices, buy more sandwiches than before because, hey, there's a free sandwich in there! The shop begins to earn more than its competitors, and garners more long-term customers who pay more of their money for the sandwiches, by exploiting a loophole in human psychology. The sandwiches are in all relevant respects identical, yet people are paying more because of a freebie scheme. Is this an ethically legitimate practice? Or is it exploitative in some way?