Years ago I appealed the assesment in Gilford and the land value was lowered.
It takes some time and effort to research other assessments. The key is to bring in examples of properties similar to yours that are assessed for less and explain why your property is not worth what they think it is.
In my case, although I had the same amount of land as other properties, my land has 50 feet of street frontage and 100 feet on the water. The triangular shape, combined with Gilford's 25 foot sideline setback, made much of my land unbuildable. The same square foot lot in a rectangular shape would have much more buildable area.
However, be aware that when they come out they will probably look for anything that is not on the tax card for your property. If you have things like a bigger dock, a tool shed, new windows, vinyl siding, or other improvements that they don't have listed, your assessment could actually go up.
In most towns they keep up with improvements when you get a building permit. The building department notifies the assessors that the improvements have been made. When significant construction is done, the assessors are notified when an occupancy permit is issued.
I have heard, but not confirmed, that sometimes people will make improvements without a permit.
I think those same people may be members of the top secret "Move a rock" club discussed here in the past.