Take something on trust
Definition 1 of 1
Pro Tip 1/3Trust vs. Gullibility
Understanding the fine line between trust and being gullible is crucial to avoid misuse of the phrase. 
I took his story on trust, but I'm not gullible to disregard the lack of evidence forever.
Pro Tip 2/3Not Always Positive
Using this phrase can sometimes imply naivety or lack of due diligence on the part of the trusting individual. 
I took his sales pitch on trust, which I now regret.
Pro Tip 3/3Relationship Context
Often used within the context of a relationship that assumes honesty or good faith. 
In a friendship, we sometimes need to take things on trust.