Got a bonus with my order. If Sainsburys do a substitute and it costs more than what you ordered, they charge the price you were originally expected to pay. So I got a pack of 9 cadbury flakes for a £1 instead of £2.50 because the cheaper pack of 4 ordered was out of stock
The balance is paid directly into my bank account. Had I sent the flakes back then I would have ended up with no flakes and a £1 voucher