One I saw had a big depositing area where you'd put your stuff to be weighed, though it did tell you to keep particularly large or heavy articles in the cart. There was a service counter right opposite, so I assume there was some measure of trust that the employees there would see if you pulled suspicious shit.

Every now and then, that scale would be picky though. Article should weigh 400-500g, but actually weighs in at 503? Yeah let's flag that for a human to check.

Blessedly, the employees generally were quick to step up, slap their access token thing on the sensor, recognise the situation and clear it without much need for interaction. Likewise with age controls, quick and no fuss. The UI had its issues but the employees at least made up for it.