The back (card stock) is the easiest way to tell if its authentic.
There are actually more fakes in circulation than authentic cards so its risky buying them blind, and like others said there are a few different kinds.
The "W517" printed on 1 type of reprint can be scuffed off easily too, so you would want to look for any signs of wear to that bottom corner just under the border line.
Good luck, show scans when you get it
