How To: Detect or Simulate Trial Mode and Present a Marketplace Offer
It is not necessary to write special code to ensure that a Marketplace offer is available to players of Xbox LIVE Community Games. By default, trial mode games that have been released will present a Marketplace offer to the player when the gameplay time limit expires. However, you might want to write special code in your game to present a Marketplace offer, or control other areas of gameplay when a game is in trial mode.
To simulate trial mode
The XNA Framework provides a property, Guide.SimulateTrialMode, that allows developers to test the behaviors of a game under trial mode conditions. When games are in trial mode, a developer might choose to limit the capabilities of the game.