Oh Emma your Sainsbury's story reminds me of the time my card was declined in Safeway (and look what happened to them eh? Nemo Me Impune Lacessit
) OH had gone on ahead to do whatever, once the stuff was beeped through, I handed over my card - No.
Try again? No
Supervisor comes - I ask her to come with me, and trolley load of goods, to the car park to find OH and his card. So we do that, all is settled etc. I ask them again to try to put my card through - No.
I was 101% sure that there was plenty in my account. Called the bank next morning - "we are so sorry - error with routine maintenance etc". I wrote them my fiercest - no not fierce, just pretty strong - letter. Costed out my embarrassment and my time in resolving the matter at £100 and sent them an invoice for that. Got it in 2 days!
But I'd still rather not have my account declined.