An optometrist sells custom-ordered eyeglasses. Assume the optometrist maintains no stock of lenses or frames (except for some sample frames to show customers), but custom orders everything from a manufacturer. Must the optometrist use the accrual method of accounting for purchases and sales of eyeglasses and lenses? For charges that include both eyeglasses and the cost of an examination?' For separate fees charged for eye examinations? Explain with references to primary sources.