Is the 220 m² figure required to be internal floor area, or could it include other space? That distinction may materially change what people send you. I’d also name the Athens areas you will consider. For quiet-market approaches, ask representatives to confirm their authority before sharing...
Be careful with neighbourhood boundaries. For retail property, crossing even a nearby boundary can change the usefulness of the comparison because the surrounding commercial setting may differ. “Athens” is probably too broad, while an extremely tight boundary may leave too few units. I’d test...