This should not be an oversimplified issue of “do trust” or “do not trust.”
There are MANY levels of trust, in between “slightly” to “completely.” You start at the lowest level and take at least one year to move someone up to the next level. Give them slightly greater litmus tests of integrity and loyalty at each step along the way. Complete, or even “almost” complete trust should be something that takes at least five years to achieve.
Obviously, you can use common sense checklists and intuition to weed out most people, before allowing them into that starting, “slight trust” level. But you better start the process soon, so you can have at least a few trustworthy allies at hand when you really need them!