The number to watch
Margin from accessories and service against margin from handsets. Handsets bring people in and rarely pay the rent; cases, cables, chargers, screen guards and repair work do. Splitting your sales report by those two groups tells you where the shop actually earns, and it usually changes what gets stocked and what gets floor space. It also tells you whether the repair side is worth the bench time it takes.
IMEI on the invoice
A phone is identified by its IMEI, and that number is what a warranty claim, a police enquiry or an exchange will be matched against. Recording it on the bill takes seconds and answers all three later. It also protects you: a customer returning a different handset from the one you sold is a known problem, and the invoice is what settles it.
Accessories are where the margin is
Handset margins are thin and everybody knows it; cases, chargers, cables, screen guards and earphones are where a mobile shop actually earns. Those are many small items that need barcodes and stock control, and they are the part most shops track worst. Getting accessory stock and margin visible per item usually changes what a shop chooses to stock within a month.
Recharges, services and repairs
Alongside sales there is repair work with parts and labour, and small service charges. Each is a line on a bill with its own rate, and keeping them recorded rather than taken as loose cash is what makes the day-end tie. Repairs also benefit from the same record-keeping as sales — what was done, on which handset, on what date — because the customer will return.