It's quite tough to tell over the internet, but a few things you can do is the following.
Make sure the name and address on the paypal/credit card matches that of the ID.
Save the ID and use google image search to ensure there isn't another ID with the same information/picture with different names on the internet.
Google search other IDs that are from the same country as the person and compare them, be sure to include the date that the ID was issued.
Screenshot the image on the ID and google image search that image.
Make sure you triple check the seal and security measures on the ID which mostly every government issued ID will have.
Good luck