It is a sad fact of life whether it be the real thing or the electronic version that you have to be aware of many scams.
The latest one to hit me (albeit annoying rather than life changing) is this:
Murcia airport departures lounge -
500 ml water purchased at Subway = 2.20 euros
500 ml water (better quality)purchased from vending machine at opposite end of departure lounge = 1 euro
Saving for walking a few mts. = 1.20 euro
Bottom line - Spanish airports have caught up with the UK with scam prices.