For me it depends on what the warning is, whether I've dealt with that kind of "problem" before or not and how serious and/or truthful/unkind I deem the warning. I've tried to warn people in real life to "be careful" around a person and they weren't then were horribly shocked and in lots of pain when that person suicided. I mostly just do a "heads up" when I get a warning about a person. I don't necessarily treat them differently but do pay more attention both to the person doing the warning and the one they warned about. The more I "trust" the person doing the warning or less I know of one or the other person, that influences my reactions too.