Unfortunately most people require very little in order to trust someone. If they "like" someone or feel "comfortable" with them they'll give away their trust! This is exactly what a conman or cheater relies upon! My advice is:
Don’t rush to give away “Trust”. Much like “Respect” it should be EARNED. Allow your mate or others to demonstrate (honesty and integrity) over-time BEFORE trusting them. So many people are in such a hurry to formulate relationships they don't want to take the time required to "truly" get to know someone.