Some stores are favored over others, based on consumer chargebacks and other costs banks must bear. But there is no conflict of interest.
There is also plenty of competition, both among banks and among processors, a thriving market of re-sellers happy to do business with any merchant who wants to take plastic.
Even here, of course, there is a public interest. Limits on consumer charges, on contract changes, interest rates and the ability of stores to refuse plastic on small transactions, are all part of the current financial regulation debate.
Conflicts of interest are not prohibited in health care payment processing and the most obvious such conflict today is in prescribing drugs. Since Caremark, the largest drug plan manager, was bought by CVS in 2006, that conflict has become more odious.
It has also become explicit with CVS deciding this week Caremark will no longer process for Walgreens, CVS' largest retail rival.
On the surface this is an argument about money, like the games of chicken played between hospitals and insurers over rates. And smaller processors like Medco and Express Scripts could in theory benefit.
But that's not the way to bet. CVS bought Caremark specifically to create vertical integration, to force people into buying their drugs through its stores or mail order operation. If that was not the motive the deal did not make sense.
The question that should be asked now is whether that deal makes sense for consumers or for the health care system as a whole. And if it doesn't, then frankly CVS Caremark's corporate ambitions should take second place.