Galaxy S5: Got my Spigen tough armor today

Each Spigen case should come with an authentication card which you'd be able to add the serial number in to see if it is legit or not.

^^Exactly this. Real Spigen accessories always come with an "Authenticator Code" and always come in Spigen branded packaging. I have used Spigen for about 2 years now and always purchase from either Spigen directly, or Amazon
 
I got that case in gold several months ago. I quite like it. It's showing some scratches from wear and tear, but it's definitely saved my S5 from hard falls.

My only complaint is that it adds considerable weight to the phone. That said I'd rather have a more bulky but protected device than a broken light one.