Jesus covered the concept quite well in the Parable of the Sower. Broadcast the seeds, and those that God wills, will grow and produce; the fate of the rest of the seeds are not our responsiblity.
You are correct, it is rank apostasy to "sell God", especially if you have to do so in ways that that would make an Amway salesman blush.
The purpose is to spread the message, and let come what may; not fill (and pay for!) mega-churches with what people WANT to hear, instead of what God wrote.
I have seen things these days that I would have never thought possible in this age: Goth and "grunge" style "preachers," covered with satanic tattoos and body piercings, playing and writhing to the most hell-inspired music imaginable - and blessing it all in the name of Jesus. Their heretical teaching and false literature; books like The Shack, which are lapped up by millions of quasi-believers, is a harbinger of the end of this Age of grace, in my opinion. Their open contempt for the "faith delivered to our fathers," who suffered, bled and died to show it approved of God, is manifested for everyone with eyes to see, but I suppose the Prince of this World has blinded many, as was foretold.