There�s no such thing as �duty free� any longer, only �duty paid�.
You can get genuine brands such as Marlboro in Greece, I believe.
Tobacco products are cheaper in Spain than in France � Belgium is cheaper than France but not as cheap as Spain. Luxembourg is about on a par with Spain I think, but it�s 200 miles from the channel ports.
There�s some info here to interest you, but Greece isn�t mentioned as far as I can see ...
http://www.day-tripper.net/pricestobacco.html
The price is the same everywhere in Spain. The other countries I�m not sure about.
The �guidelines� are that you can bring back 3200 cigarettes from another EU country if they�re for your own use. Note that the Canary Islands are not part of the EU, so the limit is only 200.