I do not check every auction for forged items. But sometimes I do and often I send them a mail. Of course this is not always met with enthusiasm. Especially, when the items are already on the internet listing. And sometimes it was the owner itself who decided which items to pick for single lot listings. I do not sent mails for collections. You should always consider collections as bundle of forgeries with the expensive (good, interesting) items already sorted out. This ends where the seller reaches the limit of his knowledge, so it is theoretically possible to make a bargain. The bad thing is, that the calculations of the collections still base on a most items are genuine projection. Together with astronomically wrong catalog prices for several items the result is often fare more than what I would consider a realistic price tag. If you want to get a good deal buying a collection you should take great care and really know what you are buying.
Yesterday I got an answer from a major auction house and I am very pleasantly surprised to get such a professional reaction. They will withdraw the lot. Another auctions house inquired about why the items are fake, I sent information, they thank me, but the items where not put from the list. Both sellers are well-known auction house in the United States.
What can we do? If you are an auction house, feel free to contact me. I already did opinions for several major auction houses. Different things are possible. From questions for a “gut feeling” based on a scan to full-page certificates based on research (detailed measurement and comparison).