A saying that I heard a long time ago, that really stuck with me (both as a business owner, and from the flipside as a customer): You can shear a sheep many times, but you can skin it only once. If you go in for the kill, and really take advantage of someone in a transaction (i.e, skin the sheep), that will likely signal the end of any (positive) transactions with that person, unless you have a monopoly or other such…
Game theory's star child, the prisoner's dilemma, also shows this principle quite nicely. As long as you plan on never working with that person again it is in your best interest to screw them over. If you plan on working with them indefiniately then the best known strategy is to treat them as they treat you, and to start off on a good foot. http://en.wikipedia.org/wiki/Tit_for_tat
We exist in a web of relationships with membership in overlapping but distinct communities. As entrepreneurs we can be seen as agents of chaos by the status quo but our aim is innovation that leaves society on balance better off.
Of course we have to make a profit for our businesses to continue, but there are other gains that come from entrepreneurship beyond the financial that lead us to invest in our employees education, to invest in our communities and to “leave a little money on the table” when dealing with partners and suppliers in the interest of good will and future relationships.
Business is situated in community and a social context: a good reputation as fair dealer committed to the values of the community, as evidenced by actual kindness and charity will create more value in the long run than treating every transaction as the last one you will ever do with the other party.