This bible of the piano marketplace is indispensable to buyers and owners of pianos, amateur and professional players alike. Hundreds of thousands of pianos are bought and sold each year, yet most people buy a piano with only the vaguest idea of what to look for as they make this major purchase. ''The Piano Book'' evaluates and compares every brand and style of piano sold in the United States. There is information on piano moving and storage, inspecting individual new and used pianos, the special market for Steinways, and sales gimmicks to watch out for. An annual supplement, sold separately, lists current prices for more than 2,500 new piano models.