Red flags:

• A captive portal asking for social login. Real airport Wi-Fi asks at most for an email, never a Facebook or Google password.
• Generic SSID without venue branding. Legit networks often say "Schiphol-WiFi" or similar.
• No HTTPS / cert warnings. Attacker portals sometimes break TLS and you get "your connection is not private".
• Two networks with near-identical names. "Schiphol_WiFi" vs "Schiphol-WiFi" — one is fake.