Don't have any experience with Leu Numismatik; however, at the German Forum I just read that this Caligula Denarius in their current auction is a Cigoi fake: https://leunumismatik.com/en/lot/29/2651/[29 You can read the arguments here: https://www.numismatikforum.de/viewtopic.php?f=6&t=11495&start=7650
Yeah I had a pretty bad experience with leu, the bad part being that I didn't win a single item. Can you believe that?
I think it is a big red flag if they are made aware of the fakes and do not pull them. Unfortunately, I think most auctions have a few fakes at this point. Fakes slip in; to me the issue is when houses don’t pull them when confronted with credible evidence.