I would have left the trolley and gone elsewhere, biker, probably uttering a loud humph as I did so . I did this from a greengrocer who wouldn't sell me half a cabbage – one of those huge ones that would feed an army. I'm sure he'd have had no difficulty selling the other half.
In defence of Asda, I shop from there online because that's all there is. No-one else will deliver to us and it's cheaper and easier and quicker to get stuff delivered than do a 42-mile round trip. Their delivery people are always scrupulously polite and, on the few occasions when I've had to ring and say that one tomato in the pack is squashed (for instance) they've refunded the price of all the tomatoes.