Freemeteo.gr has been serving Greek weather forecasts since 2008, and that kind of longevity is a strong indicator of legitimacy. The site shows up on no blacklists, has decent traffic, and uses modern infrastructure. So is freemeteo.gr a scam? Almost certainly not. But there are a couple of things worth noting before you rely on it heavily.
First, the site loads 36 external scripts — that's a lot for a weather page. Most are likely from ad networks, but it means your browser communicates with many third parties. Second, there's no privacy policy or terms of service, which is a red flag under EU law since the site probably uses cookies. If you're just looking up today's temperature in Athens, that's fine. But if you're considering a paid subscription or sharing personal info, hold off. For a free weather check, freemeteo.gr is usable, but not a model of transparency.