The notebook behind the counter, without the adding up
Keep every regular's tab right to the cent and know who has owed longest. Letting regulars pay later is normal at a corner store; the adding up is the hard part.
$6.75
Why the notebook gets hard
Pages of crossed-out numbers, a cousin who writes it differently, and a regular nobody has asked in a month.
What to write each time
Their name the way you call them, the day, and the amount, with a note like milk and bread if you want one. When they pay, what they gave you.
When they say they already paid
Never erase a line. Cross a mistake through so it still shows, and show them every line with its day. Fiao, on your phone, keeps every line, newest first.
Who to ask first
The regular whose oldest unpaid charge has waited longest. Fiao puts them first on your list of who owes.