It's been two weeks now, I am running behind the Ebay seller to get my money back which I paid for a Samsung Galaxy S8. Finally, Ebay itself pitched in and resolved the issue. From my experience, I have sorted out a couple of easy ways to find out the fake ones. If you are not really looking for a look-alike versions of the S8, you should check these before buying new or used ones....
First and the easiest way is to check for the blacked out infinite edges, as they use the exact same outer panel, they cannot give the exact same infinite-edged inner LED Screen of the original S8. Obviously, they have to cover-up the top and bottom edges, so that the LED display does not look awkward. This black stripe is visible even when the phone is switched off.
The second one will show up when you switch on the phone. You will not see the Samsung logo, but an Android logo, the sample of which is you are seeing in the second picture.
Once the home screen is on, the UI will be almost the same but you can easily find out the difference in camera quality and the battery will drain very fast like a percentage down per minute.
Save yourself from these troubles. Good Luck!!!!