That's absolutely true, of course. I've made several auction bids where the winning bid has been just £50 above mine. As you say, we never know. You need to have that line in the sand above which you will not bid. In an auction, discipline (as with other forms of investing) is essential otherwise you can get drawn into a bidding war and end up paying well over what a coin is worth. I was the underbidder on the 1791 pattern sixpence. Having recently acquired the 1788 and 1790 patterns, I had a view on what this coin was worth. My line in the sand was £650 and the coin went for £700. Well above estimate I would add. Coin collecting is a long game and another 1791 Pattern will show up sooner or later and, hopefully, I will get it then. It definitely is a long game, and a game in which one has to be very patient over protracted periods of time. Eventually an opportunity to obtain the coin you want. Then it's a matter of what you pay/bid, how good the coin is, and whether such a chance will come up again.