bjt, I collect the same sort of things you do, only in my case it's usually rare books related to a specific topic. I, too, often recognize my competitors as being members of the same organizations I belong to. Over the years I have not only corresponded with them, I've met a goodly number of them in person. It's relevant to add that several of them are millionaires who could blow me away with a single bid -- if they knew what I was bidding for.
As a rule, though, if they're interested in an item they put a bid on it. Only one or two of them are snipers, and even they don't snipe every time. The amounts of their bids are not maximums; these people
have no maximums. Rather, the amount is a function of their level of interest in the item. (Read: if it's something they don't already have, I can forget about it right now.)
So, while I'm interested to learn that these acquaintances are bidding on something I'd like to have, it's not material to me how many bids they've placed simply because if one of them wants, or can afford, something more than I do or can, why, my maximum bid means nothing. And if none of them are bidding on an item, I have learned that my maximum is usually enough and to spare to win the auction over the occasional "dabbler" that enters a bid...or two, or three.
That's my nickel's worth.