As you might be aware, Greek islands
used to have a lower VAT rate than the mainland. However this is slowly changing.
The following islands will start using mainland VAT rates as of 01-01-18:
Lesvos, Lemnos, Agios Efstratios, Chios, Psara, Oinousses, Samos, Ikaria, Kos, Kalymnos, Nisyros, Patmos, Leros, Symi, Astypalea, Chalki, Kastellorizo and Samothrace.
This means high VAT will go from 17 to 24%
Please note that other islands like Rhodes, Ios, Santorini, etc already have mainland rates.