While there is no central authority , there usually is a "pastor" who directs & teaches his flock , so the central authority is usually devolved to a parish level. When some disagree with this "leader" , they usually split and form their own group , as evidenced by the numerous "Christian fellowships" , "Assemblies of God" , Pentecostal , Evangelical and similar groups , many of whom refuse to speak or have dealings with each other.
A few years ago , I was involved in brokering a complicated property dispute when a group of "born agains" fractured into three groups under different "leaders" and fought over property rights. We were unable to appeal to the authority of any central pastoral legislative body as none existed that all three groups recognised. None would liase or discuss the matters directly, so the company I worked for organised proximity meetings and eventually we got a measure of agreement.
The best (though perhaps harsh) description I have heard , as used by an old friend of mine , is to describe "born again" style groups as "disorganised cults" (careful how you say that! ).