Hi.I always do the deep research about that watch first before met the seller.
Looks closely the picture of that watch in the official website. Zoom in. Focus on the hand shape, the dial, the date position/color, and the what written on case back on authentic watch.
See some review of that watch.
Fake watches will miss some of the detail of the authentic one.
Once you master the character the watch you lookin' for, You'll spot the difference.