“The situation is if I purchased a house at a lower price than what the previous owner has to pay, then do I have to ask the county to reassess or they will automatically reassess the tax according to the lower selling price.”
I answered that in my first sentence above…property is ALWAYS reassessed when it is sold; the new assessed value is the purchase price.
That’s one of the reasons it is stupid to pay a high asking price and get money back under the table during escrow. Not only is it FRAUD but you are going to wind up paying property tax on the recorded sale value, not the net price you paid under the table.