Polosh self checkout:

1. One cashier per 6-8 machines, on watch to take care of age verification or occasional lockuo
2. Machines do lock up when weight doesn't match...and unlock when scale decides that it's okay after all. Happens sometimes with lighter things, or when someone fucks up values in software (once met error where buns were 900g per piece xD Cashier gal was busyyyy that day, had their fixed code, but until it got into menu, they had to punch it themselves)
3. Age verification, of course, is there
4. There's only scale. Sometimes you need to also scan your receipt to leave. That's all.

Sometimes that cashier taking care of self checkouts even gets their own command center - console that can allow to give age verification without physically moving or to bypass weight alerts (useful when cashier sees from far away you carry, for example, hair bands. )