My employer uses the Challenge 25 rule. The customer and/or people they are with must look over 25, not just look over 18, or in some cases 16. This is for booze - including non alcoholic, as well as things like paracetamol, sewing scissors and some children's toys (Skylanders figures, Pokemon figures and cards - no idea why
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Regarding IDing of those who are with the person buying stuff, we are told to use our discretion. If we think they are buying alcohol etc for the rest of them, then ID the lot. Personally, I think its none of my business to monitor a legal sale, but apparently I have a "duty of care" along with my store. If I suspect the customer is drunk, no sale.
We have many testers that come from other branches to test us to ensure that we are adhering to this. I got caught because my customer was 24 years of age! Had to go through the disciplinary, which was unpleasant, but I can't moan as it is company policy.
As a cashier, I absolutely hate asking for ID. The customer can turn on you like a rabid dog because they don't agree with this "ID malarkey" and make my job so stressful. Don't get nasty with the cashier, please, they are serving you because they need the job and are terrified they'll fuck up and end up with a disciplinary like I did. We have only a short time to look discreetly at you to try and ascertain your age, so please be civil. You trap more flies with honey than with vinegar!
I ID everyone who looks around the 25 year old mark, not 18. I've learned my lesson.