Mauricio2610 made this video showing what to look for in a fake DW-6900 G-Shock. He bought what he thought was a real DW-6900 Transformers Destron watch, but it turned out to be a relatively high quality fake. There's a few key differences between a real one and a fake one. Take a look, and be careful when shopping for G-Shocks online.

BTW - some real G-Shocks do come wrapped in a clear plastic bag. It's not long and skinny like the one in this video. It surrounds the whole watch with the band closed.