23% or 18% for EU residents. This means when you buy souvenirs or anything at all for that matter you pay an extra 19%
Not just in Greece but anywhere in the world they have VAT: have the store ship for you and you avoid VAT; paying only shipping and import duties at home if applicable.
There is a form the store will provide you which will entitle you to a rebate at the airport upon departure. Plan for a lot of extra time if you go this route. You'll generally only be concerned with V.A.T. For larger purchases such as jewelry. Also see Attika Mall Shopping services Athens