Catching shill-bidders on eBay used to be one of my hobbies. I would regularly stumble-upon suspicious confluences, start examining auction and bidder histories, and from them often assemble proof that there had been shill-bidding, which proof I would then send to eBay and to the victims. I'm sure that I wasn't the only person engaging in this sort of detection.

But eBay began choking-off the data available to us. With decreasing information, it became ever harder to make the case. It became impossible even to see some of the confluences that would have triggered suspicion in the first place.

For an honest auction firm, there may be an optimal amount of shill-bidding to allow, simply because of enforcement costs. (A perfectly secure trading environment would be prohibitively expensive.) But for a dishonest firm the question is of balancing the gain that otherwise comes from allowing ending prices (and hence fees) to be thus increased, against the alienation of users who consequently reduce their spending. Access to information which both empowers volunteers to catch shill-bidders and alerts users more generally to the occurrence of shill-bidding is, as such, not in the perceived interest of a dishonest firm.

BTW, the changes that reduced our abilities to spot shill-bidders, and which made it more typically impossible for us to prove a case of shill-bidding (as well as other changes that enabled eBay to be more easily used by thieves) were primarily effected while Margaret Cushing (Meg) Whitman, now the Republican Party nominee for governor of California, was eBay's President and CEO.