Why is there such a big difference on the total assessed value and the market value amount?

On Oahu, the tax assessors don't come out and assess values every year. They are adjusted remotely and it seems, sometime, not at all. A home can be remodeled and the tax office does not know about it. Sometimes a permit is required for a remodel and then sometimes the value is updated after the permit is closed. Sometimes the tax value is higher than the market value and sometime it is lower. Often the tax records do not match the home in square footage, number of bedroom and.or number of bathrooms. I hate to say this, but it is completely random.