The best system I saw for self checkout was at a place in New Zealand about...shit. Nearly 20 years ago now.
You would walk in, scan a barcode on your store card, pick up a hand held scanner and scan the items as they went into the cart. Including fruit and veg, there was a weigh station for that. As you put stuff into the trolley you'd scan it.
When you got to the front there was a special lane. You didn't unload, you walked through and paid. Randomly - like 1 time in 5 to start with - they'd ask you to rescan so you unload into the belt, which was faster because dedicated lane. But if you always had exactly the same items that you'd scan, the trust threshold in whatever system would greenlight you. No bagging either. Just the stock boxes on a table as you left, or like us you just shove it all in crates in the boot of the car.
There was a.minor rebate in terms of store points which unlocked specials for using it but holy shit it was sooooo much faster because it moved the scan point back to you loading the cart. You could see how much you were going to spend and delete items from the scanner itself.
I am not a grocery fan so to be able to do a full week shop in under 20 minutes was awesome. As per tradition we was young and on a tight budget so it was super easy to keep tabs on how much we were spending and saving.
Then offer a discount for self checkout.