For individual cards and older booster packs and boxes, you will just have to gain a lot of experience and learn the nuances of real Pokemon products and then make educated purchases, ideally with a means of recourse if it turns out you were scammed (some kind of buyer protection program, etc)
One thing to be careful with is the political aspect of stealing something from an opponent
These cards could have had Multikicker
Actually Limited Products While Play Boosters, Commander Decks, and the Starter Kit can all be repritned as required, Collector Boosters are a different story
(I may have gotten an unfair headstart, but Galadriel in particular was so cool to me that Ive already built a Commander deck around her.) But while Turian says they did initially consider pairing these scenes directly with the previous LOTR commander products from earlier this year, they decided to make them stand on their own to allow for more design space