A lien will be sold against the property if there are any unpaid utility bills owed from the previous year, this may also include other municipal charges.
Who buys these liens? Usually people who are looking to invest money. The interest rate starts at 18%. However, if there is more than one person interested in the same parcel, they will start bidding down the interest rate. Once the bidders bid down to 0%, it will go into a premium starting at multiples of $100.