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)
Which brings us to what Lorcana is really about: its a family game, pure and simple
Elvish Mariner is a very solid three-drop, and one that ends up in quite a few decks not least Elrond Master of Healing builds
The other nice thing about Atraxa is that she lets you run every color in Magic except red, giving you more choices when it comes to building your deck
The multiplayer nature of Commander amplifies this cards power exponentially
Firstly, they could potentially look at the Brock Supporter card