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)
Search the Card Database for cards already released to discover new possibilities
(Fast-talking otaku) Here are the effects of that God as they were adapted into the OCG
5 Lorehold, The Historian Speed Isn't Everything We're choosing Lorehold, the Historian, as the worst of the Elder Dragons in Secrets of Strixhaven, although it should be noted that none of these legendary creatures are bad, so Lorehold's position on this list is a case of nitpicking against the other dragons
and that's not all, since A and C have B with their respective points, that's an extra 500 ATK boost for the A - B pair AND another 500 ATK bonus from the B - C pair