It depends on who is saying it, how they're saying, what context its in, and whether or not I do actually trust this person.
Generally, if I get this from someone I barely know, my shields are all systems go, regardless of the situation. I hate it when people say this so casually: "This is like the best movie you've ever seen, trust me." I don't know why, because intellectually, I know they're trying to convince me to see something relatively inconsequential from their point of view, but I just hate how I associate the phrase with a deceptive quality.
If its a good friend or a boyfriend or a family member, someone I truly do trust, I don't notice it much... unless I "know" they're lying somehow (and I can usually tell). That's when I get upset.