Not very reliable. The only two people I know who used one of these stores both got mischarged and never went back again. That news travels fast.
I have had them miss items and fail to charge me for them, though. Even if you want to be honest about it though, there’s really nothing that can be done, since they don’t charge you and provide you with a receipt until hours after you’ve left the store.
There are a lot of ways I’d describe the Amazon Go shopping experience. Creepy? Yes. Unsettling? Quite so. Oddly evoking the feeling of being a rat in a maze? I wouldn’t argue. But stressful? If there is one thing it is not, it’s that.
The point is bad news spreads to "I won't bother".
Lots of people use it without any issues -- if something isn't truly a dealbreaker, the "I won't bother" crowd tends to become a minority. The Law of Large Numbers will work as expected.