Curry favor by rushing down the combo or control player, then use the threat of burn spells to encourage other players to do your bidding
It started off as a $20 card, before dropping to about $5
You can also counter any Commander for just a single mana since it's cast from the Command Zone
Looking back now, 5 mana is an awful lot to ask of an enchantment that doesnt do anything when it enters the battlefield, but if allowed to sit on the battlefield after a board wipe or a couple turns of play from an Aristocrats strategy (decks that derive value from sacrificing creatures), Black Market can quickly generate game-winning amounts of black mana
Almost instantly, all the sets products sold out everywhere, which is practically unheard of for MTG
This is incredibly important since despite his strength, he only has three defense