It is quite common for the local taxing authority to attach liens to properties of homeowners who default on their property taxes. The liens are sold at tax lien sales to the highest bidders. Whoever wins gets the lien certificate, and would pay for the unpaid tax balance of the homeowner. Property owners need to pay the investors within the redemption period or lose their homes. The good thing however, investors would earn interest, depending on the state, after the homeowners redeem their properties.
People have different opinions of these investors. Some see them as saviors of debt ridden property owners, while others view them as taking advantage on the weak. Nonetheless, the whole system of tax sale is intended to be mutually beneficial and fair to both parties. The investors earn profits while the property owners keep their homes.