Because the call to Trial Maker is performed inside your codebase you should take reasonable measure to ensure that modification of this code, and this bypassing the trial system, is much harder. Microsoft .Net Framework code is compiled down to IL or Intermediate Language when you have compiled it in Visual Studio. IL is fairly easy to view, browse and modify using a number of easily obtainable tools.

Although not required when using Trial Maker it is good practice to try and secure your code base and the IL it emits to ensure your product is secure and safe. A good place to start is to search the web for .Net Framework Obfuscation, there are a number of tools out there in a lot of price ranges.