Rare high end timepieces trade in very thin markets and spreads between bid and ask can be huge. Auctions used to be the worst place for selling an independent watch as the buyers largely didn't care about them. This has changed dramatically in recent times. Still, past auctions are rarely a good indicator of current value. The book explains at length as to why that is the case for the art market. I don't want to write a whole essay on finding comparables etc, you are a long term collector and know all those things. But I would say that finding a dealer or market that has the best access to the niche buyers that might want to buy your watch and having patience are the keys to getting the best price.