How is the zakat calculated for a car upholstery and accessories shop, given the varying sale prices and the age of some displayed items? And is the zakat for upholstery work due on the fabric or on the price of the upholstery service?

If a year has passed on your merchandise, you are obligated to appraise it at its current market price, without considering the purchase price or the selling price to customers. This includes fabric if the intention is to trade in it. If the wealth reaches the nisab (minimum taxable amount) by adding whatever cash you have and other commercial goods that have also had a year pass on them, then you must pay zakat amounting to one-quarter of one-tenth (2.5%).