This was not my experience. I went to a place near Seattle several times (which is now closed). I did preset the credit card into my Amazon account. Then you enter the store, and you do have to scan something to enter the building, and then that's it. You walk in, grab your stuff, and you leave out the exit door.
In particular, there was no shopping cart, nothing pointing out sales, no scanning.
This was available during the early stages of the pandemic (when nobody was even fully sure what to do) and that was wonderful because I basically didn't have to touch anything other than the literal items I was taking home. It was so much quicker because there was no scan phase, no checkout phase, etc.. I was quite disappointed when it closed. It really was a much better experience than the self-scan-as-you-go checkout experience you described, or classic checkout, or self-checkout. That said, the whole store was simply further away than a much larger grocery store, so the convenience was outweighed by longer travel time unless I was in the area anyway. But if it were equidistant I'd have always chosen that store.
There were some things they told you. I remember I'm not supposed to pick something up, hand it to somebody else, and let that other person put it back on the shelf, because it'll confuse the software. If you put something back (eg. after reading nutritional ingredients or whatever) it should be the same person who pulled it off the shelf.
What you experienced really just sounds like what I experienced at many other grocery stores like Safeway for years that is not Just Walk Out.