Hilchos Lashon Hara chapter 7, section 7
Three concepts concerning lashon hara are similar but different in many details. These are meheiman kebei trei (a person I regard as reliable as two witnesses), mesi’ach lefi tumo (someone who speaks lashon hara conversationally without deliberate intent to divulge information) or a story that involves devorim nikorim (clear indications that it is true).
The prohibition of believing lashon hara applies even if one believes the speaker as credible as two witnesses. When we wrote earlier that one may reveal a report privately to one’s spiritual teacher or confidant if one knows that he believes one like two witnesses and that one’s spiritual teacher may believe the report and hate the person spoken of and avoid him until he knows he repented, that only applies when the story involved factors that made it permitted to speak of the person so long as he had not repented.
This includes his deliberately transgressing a sin well known to be forbidden in circumstances that cannot be judged charitably (such as the story of Tuviah in Pesachim  that involved adultery). This leniency does not apply if one could judge the deed favourably such as assuming he did it inadvertently, nor does it apply to speaking derogatorily of a person in general or saying he lacks certain positive traits (as discussed earlier 5:2) or mentioning the deeds of his forebears or relatives, or his earlier deeds. This is certainly not included in the leniency of meheman kebei trei because even if one’s report is true, it was still forbidden to speak of the person as explained earlier (4:3).
The listener too may not believe the derogatory story in such circumstances as explained earlier (6:7). (In addition to the prohibition of believing lashon hara, he will also transgress, Do not place a stumbling block before a blind person, and other negative and positive commands mentioned in the introduction. For the speaker certainly transgressed lashon hara even if he spoke the truth and the listener led him to this, for had he refused to listen the speaker would have kept silent. The more the listener believes the speaker and makes the story harmful to the victim, the more the listener transgresses through his causation of the speaker to sin.