Within the same series you can assume that cards of the same rarity are equally weighted. In other words, one rare is just as difficult to acquire as another rare in the same series. So when you are trading within the same series, it is easy to gauge the value of a card relative to the other cards in the series … common = common, uncommon = uncommon, and so forth. But what about when you are trading across different series?
Differences in the number of total cards in a series, rarity distribution between series, number of prints of a specific card, series run time, and other factors all contribute to how difficult any one card is to find. For example, the image below shows a trade between collectors with two extremely rare cards from different series. Although each card is extremely rare, these cards are not equally hard to find because of the number of prints for each card is not equal. In the example below, this extremely rare “Air Joe” card is more scarce in comparison to the extremely rare “KEV-19” card because only 200 copies of this “air Joe” card exist while there are 1200 copies of the “KEV-19” card in circulation.
Remember, some cards can have thousands of copies while others have just a few hundred or even just a few dozen … this happens with limited edition series. Some cards have no print limit at all … this happens with unlimited edition series. So when you are trading across different series, be mindful that cards of the same rarity might not be equally hard to obtain or may be more valuable to collectors because of their scarcity.