Each year the Cook County, Illinois, Treasurer’s Office holds a public auction at which it sells tax liens it has acquired on the property of delinquent taxpayers. Prospective buyers bid on the liens. The winning bidder obtains the right to purchase the lien in exchange for paying the outstanding taxes on the property. Cook County awards the liens on a rotating basis when there are tie bids, spreading the property among the bidders. To prevent people from using multiple bidders to increase their odds, the county adopted the "Single, Simultaneous Bidder Rule," which requires each "tax buying entity" to submit bids in its own name and prohibits it from using "apparent agents, employees, or related entities" to submit simultaneous bids for the same parcel. Upon registering for an auction, each bidder must submit a sworn affidavit affirming that it complies with the Single, Simultaneous Bidder Rule.