For years, I've used a service that protests my property taxes for me. Every year, the city would jack up my property valuation, they'd protest it back to where it used to be, and I'd pay them half of the delta. (They only charge you half of your savings in the first year. Everything after that is gravy. In real dollars, they typically managed to reduce my tax bill by $300 every year from the initial appraisal, and I'd pay them $150 every year in commission.)

What I like about this is that their incentives are aligned with mine. The more money they save me, the more I pay them. Conversely, if they don't think it's financially worthwhile to protest my property taxes, then they won't bother, and I pay them nothing. (It's not that I couldn't do it myself, but it's awfully nice to let somebody else deal with the problem.)