Unrelated. In this case we're not talking about the application of tools, we're talking about trust - which is widely considered to the THE most important factor in any healthy relationship. So lets try this on for size:
"If you feel you can't trust the person you've chosen to be your life partner, your relationship already has serious issues"
"Widely considered" is an interesting standard of expertise to use about relationships, since the vast majority of relationships and marriages fail. In fact the vast majority of people who get counseling report that it didn't help them.
Dr. Willard Harley is the author of His Needs, Her Needs, one of the few relationship books that was indicated by a study to actually be successful, and he has actually applied statistics and science to measure the success of his approach to marital counseling. His approach is successful in saving relationships and restoring the feeling of romantic love (or creating it if it did not previously exist).
Harley stands outside of mainstream advice on a number of issues, but as I just said, mainstream advice hasn't been demonstrated to be particularly helpful. Dr. Harley's opinion on trust is that you should not trust each other in a relationship but that instead you should invite each other to check up on each other to whatever extent you choose. In his words, snoop until snooping is boring because you've snooped enough that you know you won't find anything. When you get to that point, you'll feel trust, rather than forcing yourself to feel it irrationally (i.e., without evidence, or in contrast to what the evidence actually says).