When a seller has multiple chips and the bidding goes beyond what I want to pay, I congratulate the then high bidder, tell him I hope he wins and offer to buy or trade one of the chips if he is the winner. Whatever that may do to eBay "rules" it is not unethical since I am not conspiring against the seller.

In some cases where there have been multiple chips, I enter into an agreement with one or more people to share the cost of the chips and arrange for one of us to be the group bidder. Again, I care not about eBay's rules, but this is not unethical since I have no intent of bidding on the chips. I am depriving no dealer of a maximum profit.