My mother trained me to always keep the receipt for any purchase I made, from a carton of milk to an expensive pair of new shoes. Each week when she returned from the store she’d sit down and check off each item on her receipt and only then put it away in the cupboards and fridge. About once a year she’d spot something charged twice or over-charged and would rush back to point it out to the manager who had foolishly complimented her once on her eagle eyes.

She felt he relied on her to point out the errors of his staff and she relished the refunds and his thanks.

My father thought she was wasting her time. “It’s only a matter of pennies.”

“Look after the pennies and the pounds will look after themselves.”

He’d sigh and make an excuse t...

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