A number of airports and retailers have Duty Free loyalty programs. They’re a pretty painless way of getting a better deal.
I’m familiar with the following ones:
These loyalty programs offer varying advantages, the most appealing of which are discounts – plus joining is free. So, if you’re a frequent traveller, signing up to one or more of them is definitely worth your while. I’m a member of Heinemann and Me, and I think it’s very good. They communicate regularly with pretty good offers, but they don’t inundate you with emails.