The fact that a situation falls under one of the previously listed categories does not necessarily mean that discussing it constitutes constructive speech. Several conditions must be met.
(1) The first set of conditions deals with verification of facts. It is absolutely forbidden to make any critical statement about a person on the basis of information obtained through hearsay. Only through first-hand information may one assume that a Jew’s character or behavior is wanting. (An exception would be where one seeks to protect someone from potential harm; such instances would permit one to pass on second-hand information. This will be discussed later.)
(2) Even if one has witnessed seemingly unacceptable behavior, he must not hastily pass judgment on what has occurred. An incident taken out of context can be terribly misleading, both as a reflection on an individual’s character as well as in determining who is right in a dispute between parties. Circumstances must be carefully investigated before one can be sure that he understands a situation correctly. Above all, before concluding that a person has, in fact, transgressed Jewish law, one must be knowledgeable of the relevant halachos.
Sefer Chofetz Chaim, 13 Chashvan, page 134