Depreciation is much bigger in the UK because supply outstrips demand but that does not happen in Greece. People changing at 1 year old, because they must have this year's plate, or 3 years old, because they don't want to get involved in the MoT test, or lease cars coming onto the market because the term of the lease is up are not really factors in Greece. People used to buy a car new and keep it until it was worn out, which often meant 20 to 25 years. That has come down in recent years but the length of time people keep a new car on average is still much longer in Greece than in the UK.
In the UK I tried to buy cars at 3 years old, because the price is about 50 % down from new, and then sell before they were ten years old, when the repair costs start to increase. The first car that I bought in Greece at 3 years old was 15 years old when I sold it. The second one that I bought here at 3 years old is now 13 years old and I have no intention of selling it in the foreseeable future. With the first car I was lucky. It was an ex-company car owned by an American subsidiary in Greece with which the company I worked for had a good relationship. They used a standard depreciation table rather than market value so I did get it for about 50 % of the new price. The second one I bought from somebody returning to the UK so it wasn't 50 % of the new price but cheaper than a Greek garage would have charged me for the same car.
You are not going to find a car here as cheaply as you would in the UK but you can find ones at decent prices if you search around. I think agents in Athens tend to charge lower prices and it is no big deal to buy there.
PS Some makes of car tend to be more expensive in Greece than others when new. It is probably worth looking at new prices on Autotriti
and then look for models that start off cheaper. Car.gr
will give you a wider perspective than a single Crete agent.