Good Afternoon pinoypride,
I have been collecting the Pathfinder and Protrek line of watches for quite some time. The watch you are asking about is a Pathfinder (PAG 240T-7CR) with the metallic band from Casio ABC line of watches. It is not a G-Shock. Casio did release its first G-Shock with ABC capabilities and is model number GW-9400-1CR and its name is "The Rangeman."
I have bought a great majority of my watches through Amazon and I have never had an issue with the authenticity of the watches being sold through them. If you should happen to spot a fake, all you have to do is call customer service and let them know. They will act quickly on the issue for they pride themselves on providing the highest customer satisfaction.
I hope this information has help you. If you have any questions in regards to either watches just write me and let me know what you need help. If not you can ask any of my comrades here on our forum. There is some really KNOWLEDAGLE guys on G-Shocks and Pathfinder's / Protrek's here. I would kindly remind you there is a specific ettiquete you have to follow. In other words you can gain more with a drop of honey than a drop of gel. Patience is a virtue, remember all of us here work at sometime during the day, and we all come in here and hang out and share our love, passion and knowledge on these awesome watches.
Hope you have a good day.