I use to see so many guys at different cons selling obvious forgeries. Whenever I told them about them it rarely went well. It was always the what do you know or you weren't there spiel. One guy told me to leave his table or he'd have me thrown out.
When a guy is selling Harrison Ford signed pics for $95 and Elvis signed albums for $350, odds are he knows he's selling suspect material. Probably not much to be accomplished by telling him.