It clearly shows that the app is available for purchase, but it also has a trial version.
Let’s see the same app on the web interface of the Store:
The web interface also shows that you should pay for the app, but nothing about the trial version. It turned out, that the webstore web store assumes that all paid apps have a trial version and only shows that it is free or paid.
If the visitor uses Metro style IE, she will see an additional button, and if she clicks on it, the Store app will show all the details:
Did you notice the two “if”s?
As a developer all you can do now is to provide some info about the trial version in the description of your app. What do you think, the users will learn that they have to look for it there?