Its especially useful for niche trades such as lucky trades, shinies, or specific IV requirements where dedicated attention matters
They already established they want the card game to be a real card game, so with the advent of that, chances are, the game will get multiplayer, either to show off your store to friends, or to challenge them to fights using said high cost cards, showing cards off is a great way to experience card games.
There's a great selection of different TCG and sports cards
Normally, I wouldnt consider such an article as Underground Material (I have an episode centered around the topic of PTCGO this week), but in my time with the program Ive found that there is a definite science to getting your deck as cheaply and quickly as possible
41 of these cards are non-exclusive to a specific version, while all the others are only found in specific pack types
As for the design process, Dragon Shield made it extremely simple and intuitive