If your property taxes, water charges, or other charges against your property are not paid, these charges can become tax liens that may be sold in a tax lien sale. Each year NYC Finance sells tax liens. If your property has unpaid debt that qualifies for the lien sale, NYC Dept. of Finance will sell your lien debt (the amount owed) to an authorized buyer. A lien servicing company, on behalf of the buyer, adds more fees and interest to your debt, so it is much better to take care of your debt before it is sold.
For more information visit; http://www.wikihow.com/Buy-a-Tax-Lien-Certificate http://money.cnn.com/2012/03/05/real_estate/tax-liens/index.htm