Charter promoters have long argued that traditional forms of accountability like auditing and financial and academic oversight are unnecessary because the magic of the market will hold them accountable. If parents enroll their children, that is all the accountability that is necessary.

Peter Greene explains in this article why the market does not create accountability for charter schools. 

It has been a rough day at my house. The IRS is auditing me and needs me to send them money now. My computer has a virus. My Microsoft Windows is expired and will shut down soon. And if I don’t re-enter my personal information, my email, Netflix, and bank accounts will all be shut down. The only good news is that I still have a chance to buy great insurance, and I’m still waiting to hear back from that Nigerian prince. 
Why do phone and online scammers keep at it, long after the vast majority of folks have heard about the most common scams, and even your mother knows not to say “yes” to a robocaller? Why don’t these scammers think, “Time to change my business model?” Because if scammers get a return on even one hit out of 10,000, that’s more than enough to keep them in business.
Charter school advocates have long argued that one reason that charters don’t need much formal government oversight is that they are subject to a greater accountability, that they must answer to parents who can “vote with their feet.” But the feet of charter parents don’t exert very much pressure.
The vast majority of charter school operators have nothing in common with phone scammers, but the same basic market principle applies.
Take, for instance, the Success Academy chain of New York City. New York City schools have an enrollment of roughly 1.1 million students; Success Academy has roughly 18,000, plus a waiting list. Over 1 million students have already voted with their feet against Success Academy, but there are no signs that SA head Eva Moskowitz is worried about tweaking the school’s approach to entice some of those million students to “vote” differently. She doesn’t need them. Nor do I suspect she’d bat an eye if even a dozen parents came to her and said, “Change this rule or we are pulling our kids out of here.” 
What do you think she would say?