We have seen (Day 140) that secondhand information which would ordinarily be considered rechilus may be communicated for a constructive purpose provided that it is not presented as fact. Regarding loshon hora, however, communicating secondhand information for a constructive purpose was prohibited in most cases (see Day 43).
The Chofetz Chaim explains that while achieving a positive result on the basis of firsthand information is justified even when the chances for success are minimal, secondhand information may be used only when one can assume that the intended result will almost certainly be achieved. Consequently, one may inform one party in a prospective shidduch (marriage match) or business partnership of possible major problems regarding the other party (see Day 83) on the basis of hearsay, since such information will probably be taken very seriously. For the same reason, one may warn a potential victim of impending danger on the basis of secondhand information. Conversely, one cannot publicize the alleged unethical behavior of an individual with the hope that social pressure will encourage him to change his ways or reimburse his victims; this would be permissible only when one has witness to such behavior. The effectiveness of social pressure in persuading people to change their ways is far too limited to justify relating secondhand negative information – even if it is clearly stated that the information has not been verified.