Airports can be stressful places and having to pull out your boarding pass when you are buying a sandwich or magazine is one of the little things that can add to the annoyance.
It seems like something which might be a security measure - but the actual reason why you are asked to present your pass has nothing to do with any laws or airport rules, it's so that retailers can avoid paying VAT on some sales.
In the UK The Independent has led calls for retailers to be more transparent about why personal information on boarding passes is demanded from customers.
Shops in airports are not required to pay VAT on any sales to individuals who are travelling outside of the European Union.
This means the retailers can make savings of more than a fifth on sales, usually without passing any of the benefit on to customers.
“I think the problem here is that the retailers are not being straight with the public,” said the consumer affairs expert, Paul Lewis.
The presenter of the BBC's Money Box Live continued: “They are asking to see passengers’ boarding cards but not telling them that this is so they can make more money by not paying the VAT on what they’re selling. What of course they should be doing is passing on the savings that they make to the passengers who are travelling outside Europe."
Most franchises charge the same price in their airport outlets as they do in city centre stores - and those who do offer cheaper prices do not come close to the savings that these stores make by not having to pay tax on many sales.
There are however some exceptions such as Harrods in UK airports which actively passes on these savings in airport outlets.