Thanks for your reply. Were you able to negociate with the Greek authorities over the valuation of your boat or did they just use the bill of sale? I understand that VAT is about 18% in Greece.
Sorry to disagree with you, but I think that comparing the purchase of a boat from Greece (which is in the EU), with a purchase from Turkey (currently outside the EU), is not at all relevant. The rules are entirely different for each case.
VAT on 2nd hand yachts is a real legislative minefield. See my reply on the Scuttlebutt for where I found the best information.