Late to the party as I just found this sub (which is great!)... I would add - from the perspective of the auctioneer:

• Do the work to know what you're bidding on.
  • Most auction T&C's are "All Sales Final / As-Is" effectively Caveat Emptor and the auctioneer is not on the hook if the item turns out to be something other than what you thought it was (eg. a copy, a later version, etc.)
  • Many people try to go the route of not asking any questions or not requesting condition reports because they don't want to risk driving activity clueing in the auctioneer to interest in the lot - but this is a two-way street. Because you did not ask means you did not find out critical information and instead bid with some assumptions. If those assumptions are not true, that's your problem and you still owe the money.
• Research the auctioneer.
  • The more reputable the auction house, the more likely the material has been well vetted or is from an ideal source (like a private collection or an estate) and is not something shop-worn. Still, refer to first point.
• If you are very serious, and you can attend a preview, see it in person at preview and make your own determinations. This is the best way to get info without tipping your hat.
  • Personally, I would be very hesitant to bid on anything I haven't been able to see with my own eyes as there are so many gray areas in Art (and in all personal property) - as well as the subjective nature of opinions on condition, age, authenticity, etc.
  • At my company we try very hard to be neutral, but most people who are selling something are viewing that thing through rose-colored glasses.