A buy-sell agreement can have an important purpose in an estate plan. It is an agreement used by business owners to sell the interest of a deceased owner to the remaining owners for a pre-determined price or by use of a pre-determined formula. The advantages are allowing the remaining owners to retain control of the business and assuring a definite price and buyer under mutually agreeable conditions.What about the value of the business interest for estate tax purposes? Will the buy-sell price control for estate tax purposes? It will if the stated price in the buy-sell agreement was entered into for a bona fide business arrangement and was not a testamentary substitute intending to transfer the interest for less than fair and adequate consideration.