Visit EU-Customs within three months after your purchase to get a Customs stamp. Be aware that Customs will only stamp your receipts the day of your departure, and in the last EU-country you visit before leaving the EU.
To get a Customs stamp on your purchase receipts, show them your purchases, passport and airplane ticket. After a Customs officer has checked your documents (he/she may require to see the goods), the officer will stamp and validate your purchase receipts for a VAT refund. Check Customs at Schiphol
EU-Customs will need proof that you are living in a non-EU country. If you have an EU-passport, you will need to show a visa, work permit or other legal document stating your non-EU residency. EU-Customs may check if you are registered in the EU through their own database.