That is not necessarily true! Some perfume will be cheaper at the airport shop if it is a special promotion. On the plane choice is limited. I do not buy any old perfume, only exactly what I want and I check the price beforehand. For example it is difficult to buy Chanel Chance discounted in the UK but it is usually cheaper at the airport. However sites like allbeauty may have lesser brands for a better price than the airport. You could always buy at the airport and use that perfume all holiday. I often do that. If you are going from T5 Heathrow you have a mind boggling choice too so if you are not sure what you like, you can spend a fun hour trying them out.