The heart of her husband safely trusts her, so he will have no lack of gain.

The key word here is “safely.” It is not about whether he chooses to trust her; it is about her being trustworthy. She has his best interest at heart.  She keeps to herself the things he tells her in confidence.  This is probably also a commentary on her general competence – I can’t imagine a husband “safely trusting” a wife who may have burned down the house cooking dinner or dropped the baby on his head while he was away at work!  (This is not to say that stuff doesn’t happen sometimes – just that if this is his expectation of what occurs during the day, due to her gross incompetence, lack of common sense, etc. he probably is not able to trust her.) The next verse provides some additional insight into this one, as well.