I've always protested it with the county myself. The minimum fee with using a company was just never worth it. I've done it every year I've lived in my house (7 years) and had had varying degrees of success every year. The first year is always the hardest because you basically need to build a master list of comps in your neighborhood/surrounding area. Then you just update it every year. I used to just argue that my property was valued much higher than homes across the street or in other areas of the neighborhood and it always worked. Seemed like they just gave me a break for trying. A few years ago I looked closer at what they would send me and took notice of how they value each home and noticed that they were applying an incorrect home characteristics to my house. Basically their system had that my home was 50-75% stone and the rest stucco when in actuality it is the opposite. That alone was being valued at $15k. The morons just never update so I have a great argument each year. I also benefit from the fact that there are about 10 other homes in my neighborhood that have the same floor plan but with varying elevations. Those are easy comps because they are all below my value. I include a picture of the other house and then mine and conclude that they are basically the exact same home but they are being assessed at sometimes a $25k difference.

In short, I would never miss an opportunity to protest and unless you own a million dollar home, using a protest service just isn't worth it. You'll learn the process and what works and what doesn't. Build a spreadsheet and keep pictures of your home and comps in a file and use those every year.