I'm thinking of getting my first GShock since an old used digital in junior high. I'm considering buying from Amazon where they have a fantastic price and good reviews, the company has over 54,000 rating which I'm guessing is their star rating. Only one other company comes close to that and is $20 more for the GShock Im looking at. There are over ten companies selling it, the highest price is $30 more. When I get it how can I tell if it's authentic? I trust Amazon to back what they sell so I don't mind trying it. Advice?