Fake Coin, Advice Sought On How To Handle Major Auction House

As a sidenote I scrutinized this coin, weight checked out, and it did not come off as fake. However, I am not an expert and the value was such that sending it to David Sear seemed overkill. The auction house sold it twice now and it comes from the collection of a premiere experienced collector originally. So when it was sold again, the new buyer questioned it and on closer look the auction house confirmed it was not genuine. In the end since I was selling it anyway, getting a full refund was fine by me.