As false doctrines and teachers abounded, there must be a way to tell who is false and who is not. Probably during that time, much of that was done by reputation and/or who they studied under, assuming that what they were taught by their teachers was what they themselves still believed and clung to. A good name is rather to be chosen than great riches. Another way was by what doctrine they held to. Jesus and Paul were all concerned about feeding His sheep so that they would know truth so that if someone came around teaching something different, they would be ashamed.
Nowadays, there are many oneness organizations that hold to the basic doctrines of belief in one God,
Acts 2:38 salvation, Jesus Name baptism for the remission of sins, baptism of the Holy Ghost, and holiness.
If a traveling evangelist made himself available to a local church, probably that Pastor would ask for references - which speaks to his reputation and having a good name - and what basic doctrines he holds to. I can't imagine a 3 stepper
Acts 2:38 church allowing a 1 stepper evangelist to come preach to some possible sinner, never been-born again people in his congregation.
So reputation and basic doctrines and holiness is probably what certain pastors look for nowadays in determining whether to let a traveling evangelist that they haven't heard of before, stand behind his pulpit.