Many of the 'self-checkout' machines are really bad at what they do. Put the items on a scale as you scan them, but don't put your own bag on the scale ... so you can bag the item after it's scanned, saving repeating that motion for each item ... or it will bitch at you. Repeatedly. (And the 'watchperson' comes over sounding accusatory.)

The store can damn well afford to pay someone to scan and bag the items, while I do the loyalty-card, payment-card cha-cha. The store isn't paying me to do all this shit.