Follow every guitar, piano and school rental by serial number from the trade-in to the sale.

A music store holds two kinds of stock under one roof. Strings, reeds, picks and cables move in hundreds, while a violin, a saxophone or a digital piano is a single item with its own serial number and history. One counter has to price, sell and service both. The second kind carries the money.

Used instruments make it harder. A trade-in arrives with a condition and a price, goes to the bench, and leaves again as a second-hand listing. Rentals for schools run alongside. When a term ends, the instrument is hard to find.

The sales staff greet players, let them try an instrument and quote a price. Customers bring in an old guitar for a trade-in. The buyer inspects it, grades it and offers a credit. Price is a guess. A teacher phones to ask for ten student violins for the new term, in three sizes, with a case and a bow each.

The workshop does setups, restrings, fret dressing, repads and tuning, taking each job in at the bench with a tag. A rental clerk hands out instruments against a signed form and takes them back when the term ends. Some never return. Buyers order from distributors, check cartons against delivery notes and enter serial numbers by hand. Rooms upstairs for lessons are booked hour by hour, and every teacher is paid a cut of the fees at month end.