Each country has an import free threshold. This threshold varies per country. If your purchase amount exceeds this threshold, you will be required to declare your goods and pay import duties upon arrival in your country of destination. The thresholds of most countries can be found here.
For more specific information on import duties for the country you are exporting too, please visit their government website for more information.
Declaring goods is a responsibility every traveler has, whether the VAT is reclaimed or not. Once you leave the EU, it is up to customs in your non-EU home country to check that travellers declare their goods.