Before commenting, let me say the situations (friends, for example) are not the same in every case, and I am making off the cuff remarks here; with more time, I might put things differently.

It is definitely advantageous for the bidders to make a bidding group for a large lot that is amenable to being split up -- say, 82 rare chips, all the same.

It is also advantageous for, say, two friendly collectors to bid as a group for one desirable chip, and then after the auction to conduct their own private auction for the chip or "flip a coin" to see who gets it, like whether the next day's Dow Jones Industrial average is odd or even.

Each case is different. If approached, someone could simply decline joining a bidding group for that particular chip, but join on future auctions.

Robert
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Helen Gilbert and Nat Pendleton (center) at low roulette table in "Death Valley" (1946).
http://www.antiquegamblingchips.com/StillsC_FemaleStars.htm