[throwaway672000]

>to check it, they would send in 25 year olds

Well, not sure if typo, but the margin of error is the point surely? It's fine that 23 year olds who look 26 slip through as long as 17 year olds who look 23 don't. Otherwise the store is effectively saying "we expect your judgement to be up to 7 years too high and account for that" but also "you're in trouble if your judgement is 1 year too high"

[patmcc]

Two things - first, no typo, but in my jurisdiction legal alcohol age is 19, so +6 years is the margin of error (at that particular set of stores, anyway). Second, it's more about changing how the question is framed in the mind of the clerk. Instead of "is this person definitely over 19?" it's "is this person definitely over 25?" - which has a much safer error rate if there's a big penalty for selling liquor to minors and a small penalty for asking for ID when you don't need to.