In a narrower sense reliability is attached to the implementation of an announced action or to compliance with other arrangements or appointments. Here I want to look with you on the reliability in a broader sense: The reliability even in the situation when you cannot meet the announced action or promise or you don´t want to meet it.
How do you communicate that? Looking for an apology or even an excuse? Waiting until the last moment in the hope that something frees you from this uncomfortable situation? Conveying it precautionary with a tiny aggressive touch, so that the other´s anger or disappointment is redirected immediately? Playing your freedom of choice down? Defining yourself as a victim of circumstances? What would be the most reliable way to communicate your non-compliance-will?