The sample code on page http://msdn.microsoft.com/en-us/library/ff967559(v=VS.92).aspx where the page is titled How to: Implement the Trial Experience in Your Application for Windows Phone - the sample code is shown as using Microsoft.Phone.Tasks;
public MarketplaceDetailTask detailTask = new MarketplaceDetailTask();
private void buy_now_Click(object sender, RoutedEventArgs e){
detailTask.Show();
}

leads a new developer to misinterpret this as the exact code that should be in the click event, which isn't the case. Please use greyed-out, ellipsed text (or something like that) to indicate that text is missing and what the text is for and what it does.

All three snippets of sample code should work together in terms of names and purposes, which they currently don't.