On stage, actors sometimes forget who they're talking to. Here's a helpful hack_
Everyone is either with you (allies of your character).... or against you (antagonists).
Once you realize the person in the scene isn't to be trusted, take everything they say as a lie. Examine everything they say as their attempt to manipulate you into doing something against your interests. i.e. not what YOU want.
If they are to be trusted, then trust them fully. Look to them for advice, guidance, counsel, or give it.
Lastly, anyone on stage may immediately change sides to the other. Until you know who's who and their motivations, it's up to your character's (i.e. your) intuition to determine how to treat them.
There's a subtlety to trust reactions, but it comes intuitively when you remind yourself that the person you're talking to (or about) is someone you don't trust.
As an advancement of the guideline, it's also interesting to note that, from their perspective, they shouldn't trust you, or your motivations. Attempts to earn their trust, ignore their mistrust, or deceive their trust by manipulating them and realizing their level of trust in you is just as subtle and artful.