I am not from Greece, so can't comment, but I agree with you and bet it's happening.
Definitely has been happening here as long as I can remember.
People pickup cartons coming back from US trips and resell them,, you can get it at less than half price locally. Cartons can be had for 30-40$ usd at duty free.
I have coworkers who travel 90%, they always bring back cartons and charge $20 markup.
Bringing cartons across from another province as they have less taxes.
Buying from the "native reserves" as it's tax free.
Buy from Asian convenience store, cause they are importing illegally at a lower cost.
Heck, not sure how easy u can pass customs nowadays, but you could buy cartons online from europe 5-10 years ago with ease illegally.
There's many options.
Smoking is a convenient crutch for people addicted, it's crazy that something that can make you feel like shit, but can also temporarily make you feel better.
(Mindset of a smoker... I could chain smoke, feel like crap. My next thought is, maybe I should have another one).
If anyone wants to quit, I suggest the following as mandatory Reading:
Alan Carr: easy way quit smoking (many iterations on title).
This is a magnificent book that has helped many people I know, including myself.
Helps you understand the addiction, the hold it has over you (which is mostlt mental), and helps put you in the right mind frame to quit.