Municipalities may abate taxes "for good cause shown," per RSA 76:16. Good cause is generally established by proving your property's assessment is either inaccurate or disproportionate. You need to prove at least one of the following:
Items that affect value are incorrect on your property record, such as you have 1 ½ bathrooms, not 2, your garage measures 24x26, not 24x28, or a survey shows your acreage is different.
The assessed value is accurate but inequitable, because it is higher than other similar properties.
The assessed value is too high; similar properties have been selling for less than your equalized assessment (see below for how to determine your equalized assessment), and/or you have a professional appraisal indicating a lesser value.
Good cause can also be established by showing poverty and inability to pay the tax. If you are claiming this reason, you must state in detail why an abatement of taxes is appropriate as opposed to some other relief, such as relocating, refinancing, or obtaining some alternative public assistance.