In the EU airports I am familiar with you either can not buy any of the 'taxfree' or specially priced 'buy before you fly' items when coming through the airport shopping area on your way out, as only with a valid boarding pass (and it will be scanned) you can buy. Or you are not coming through the normal shopping area at all.
There are airports with 'shops on arrival' but you discounted those.
There are also shops which advertise that you can buy on your way out and collect on your return, I assume you will not look for those as well.
But as there are very many airports and each has its own layout and rules, you may find the odd airport which does allow you to buy on arrival.
There is a way around 'not having a boarding pass' when you arrive by buying the cheapest ticket (and mostly you need to do that far in advance) or by having a hidden city ticket, throwing away your last leg after you have done your shopping.
Before you spend money in the airport, do check that the offers are better than you would get in the cities. For the items that I might buy I am not at all convinced they are cheaper in the airport, especially if you do include lower guaranty level or awkwardness of having to return to said airport to get service or replacements.
Airport prices are mostly aimed at street prices outside the country, and often to a specific country.