The Foundation for Economic Education has an informative article out, regarding what's necessary for a "free market" to function. After I read it, I realized that it explains what I couldn't, regarding how and why markets and competition work.
In a free market, “Scrooge-like behavior” is certainly permissible as long as it doesn’t initiate violence or fraud. But where do the high quality, low price, and innovation we associate with the free market come from? Well, as most economists will tell you, much of it comes from the fear of competition. If you cut corners and charge consistently high prices, even though you may be within your rights to do so, many free-market advocates would rightly point out that free entry and hungry entrepreneurs will tend to keep you in line. That’s important, but it’s not the whole story; not by a long shot.
Honesty and fair play, trust and reciprocity, are principles that FEE has always upheld as crucial parts of the “foundation of economics.” They go far beyond the indispensable but bare minimum of private ownership of property, free trade, and individual self-seeking—or what one might call “free-market minimalism.”
... A chapter called “Murder, Reciprocity, and Trust” in Paul Seabright’s excellent book The Company of Strangers, proposes that we divide society into “calculators” and “reciprocators.” A pure calculator is the economic-man caricature who is ready to act opportunistically (with guile) at any moment. A reciprocator is someone who is going to repay what is done to her, good or bad, no matter what. If someone cheats a reciprocator, she’ll go to the ends of the earth to make him pay; if someone does her a favor, she’s going to return it, even at great inconvenience to herself. A reciprocator keeps her promises.
Seabright argues that even pure calculators would have to pretend to be reciprocators at least sometimes lest everyone, including other pure calculators, shun her. It’s people with a norm of reciprocity, an internalized rule to give tit-for-tat even when you don’t have to, who are critical to the free market.
Note also, however, that if B reciprocates and repays A, A must have first trusted that B would indeed repay her. Trust means here that A is willing to make herself vulnerable to B’s opportunistically not keeping his promise. Trust is the flip side of reciprocity.
But if A is too trusting, calculators will take advantage of her, which gives A an incentive to be a calculator at least part of the time. That’s why Seabright argues that in the real world people have an incentive to find the right balance between opportunism and trust/reciprocity.
... The free market is a great engine of discovery and development because the people in it have the opportunity and the willingness to take chances. Bringing many strangers together who have diverse knowledge, skills, and tastes—which we find markets doing around the world—presents the opportunity. Being willing to trust people we don’t know—new employers, suppliers, coworkers, customers, neighbors, and friends—enables us to take advantage of those opportunities.
Of course, sometimes trusting someone who turns out to be untrustworthy hurts us. But even those unpleasant experiences teach us something: we learn the circumstances under which people are trustworthy or not. That’s valuable knowledge we would never have learned if we were unwilling to trust in the first place.
If we are unwilling to trust when the opportunity arises, if we are mere economizing calculators, we shouldn’t expect the free market nor any other system to develop the complex division of knowledge and labor necessary to achieve real prosperity. The greatness of the free market, however, is that, more than any other system that we know, it enables us to learn and to grow, even as it allows us to flourish.