There is a theory that the famous "Mask of Agamemnon" from the Shaft Graves at Mycenae is not ancient but a fake done at Heinrich Schliemann's behest, but so far I don't think it has a lot of adherents. I've read some accounts of Schliemann's excavations, and the whole thing does come across as very iffy. He just kind of pulled that thing out of, uh, nowhere. It seems strange to me that he retains the credibility that he does.
There are some serious questions about Schliemann's veracity. The doubts about the authenticity of the mask seem to have been raised first by William Calder III, a professor of Classics at the University of Illinois at Urbana-Champaign. David Traill has also done work on this question.
Google "behind the mask of Agamemnon" and it will take you to an issue of Archaeology where several experts debate the issue.