The Talmud (Niddah 61a) makes it clear that although negative information should not be accepted as fact, one can and should act to protect himself and others on the chance that it may be true. Just as it is naïve and wrong to believe the loshon hora one hears, so too it is naïve and irresponsible to totally ignore a report which could save oneself or others from possible harm or anguish.
On a personal level, one’s relationship with the subject of the negative report should not change. Chances are the statement was inaccurate, if not altogether false. One’s behavior towards the individual should, therefore, not be affected at all, and one should continue to show him kindness and assist him as in the past. On a practical level, one should investigate the matter and protect himself against any possible harm that could result should the report prove true.
If, for example, one hears that an acquaintance is dishonest, it is forbidden to think of him as such – but one should keep his wallet in a safe place when that person is around! If one is told that a person who accepts charity is actually well-to-do, one should not stop assisting him until the matter has been investigated and it has been determined beyond doubt that he is not deserving of assistance.