If you own real estate in Hall County, you’ll probably find out soon what the county government thinks it is worth. More than 74,100 property tax assessment notices were mailed to county property owners Friday, and they may show — for the first time in several years — a taxable value on real estate that looks more like its selling price. The change is due in part to a major effort at reevaluating the county’s property and a the effect of a new state law that requires local tax officials to tax property owners on the sale price of their home for at least the first year after they buy.