In 1981, when I was young, I walked across the bridge over the Maritsa river near Ipsala, crossing from Turkey to Greece. There were two rather scruffy & relaxed young Turkish soldiers on the bridge, with rifles slung. They amiably asked where I was from, shook my hand, & wished me well.
I walked across the painted line in the middle of the bridge, & was confronted by three immaculate Greek soldiers, glaring at me as if I was their worst enemy & holding rifles as if they were ready to use them. The NCO in the lead held out a hand & almost spat "Passport!". He looked at it then directed me to the immigration & customs office at the end of the bridge. I glanced back & saw the Turks. They shrugged.
Greek immigration & customs treated me like dirt, scowling, asking me several times if I had any drugs, & riflng through my rucksack, mixing everything in it up but not doing a serious search.
It looked as if they thought entering Greece from Turkey was a crime. Or maybe it was being friendly with the Turkish soldiers.
Note that my general experience of Greece & Greeks is friendliness & boundless hospitality. I've worked in Greece, with Greeks, & been there on holidays. That greeting stands out because it was so untypical. My next close encounter with a Greek was a young man who came out of his house to ask if I needed any help, when I was standing beside a bus stop on the edge of Alexandroupolis (nearest significant town to the border) trying to work out if it was the right one for Thessaloniki & when the next bus was. He told me it was the right stop, but the timetable was only for local buses. Then he wandered off, returning after a little while with two cold Cokes (it was a hot day & there was no shade) to tell me that a bus was due soon. He'd phoned & checked. We sat on the kerb & chatted while drinking the Cokes, until the bus arrived. That's more typical of my experiences with both Greeks & Turks. But that border crossing . . . . I'm sure it was due to where I was coming from, my interactions with the Turks, or both.