It sounds like your friend did a 'temporary import' - this meant the paperwork had to be re submitted regularly.
Even for those who tried to do this it was pretty difficult with law changes and customs not knowing what to do.
Doubtless your friend also had to pay an 'easement' to get his goods into the country which was divvied up at customs.
This i believe led to a lot of files being 'buried'.
Unfortunately Izmir eventually had a new port director appointed and he seems to have made it his mission to close all these files and levy hefty fines and costs to regularise the imports to permanent status.
If your friends case has already been taken to court ( he might not necessarily know about it) he has very little time to appeal.
There is a substantial discount for paying quickly.
The consulate tried to assist when these first started coming to light as they had good relations with the old port director, unfortunately the new one would not play ball.
i wish your friend luck but in all honesty i dont think he will have much choice but to pay up and do so within the hefty discount period, he will need a port agent again to complete the paperwork also - his original importers should help him there.