>>937486Also I'm friends with many people who are yugioh vendors, to answer your initial question.
You can make money bulk buying yugioh cards and repacking them on ebay as "random" lots of a certain rarity (super, ultra, etc).
All cards you pack will essentially be worthless and cost you next to nothing but there's quite a bit of effort involved acquiring the cards initially and physically repacking them.
The other method is significantly more profitable but involves buying card collections from players who are quitting the game at a heavily discounted rate, if you have decent knowledge of the game and card prices you can make decent money doing this.