The city relies on property tax revenue for a large portion of its budget; when property owners don't pay up the city can't pay for fire, police, schools and other essential municipal services. The city needs a means to make sure scofflaws pay up, and the tax lien process has traditionally been seen as offering an efficient way to accomplish that. The city sells tax lien certificates to third-party investors for cash up-front and lets the investors become de facto tax collectors — with the ability to charge exorbitant interest and fees. If the homeowners don't pay up, the investors can file to foreclose on the property and seize all the equity their owners have built up over the years. In many ways, it's just as egregious as the flawed ground rent system that prompted a rush to reform after a Sun investigation several years ago, but this time, it's the government that's doing it.