If you are flying within the EU there are no restrictions on the amount you can purchase for personal use (there are some guidelines that exist for these amounts).
If you are travelling outside the EU, customs allowances do apply and these vary by destination. Look up your destination on World Duty Free’s Custom Allowances page for more details.
When you make a purchase you will be asked to present your boarding card, this is to ensure the items purchased are acceptable for your final destination.
World Duty Free staff may advise on the items and quantity purchased, but it is always your responsibility to check if these are within the customs allowance quantity guidelines for your destination.