These are obvious signs but I still want to say them here as a reminder because I still see people getting scammed. When the person you're dealing with doesn't agree to use escrow. Also the threads on the digital goods section that gets locked by the author after its bumped.

You don't need to get scammed just to understand how they can scam you. Following other's advice can help as most scammers use the same trick in scamming because there's always new people coming in to crypto.