People were genuinely upset at the Windgrace deck, and I do understand why now
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
Case Studies : Yu-Gi-Oh
Those that lock opponents out of the game, giving you time to win at your leisurethink Solemnity plus Decree of Silence, Narset, Parter of Veils and Wheel effects, or Stax pieces, like Winter Orb and Stasis
Fable of the Mirror-Breaker and Big Score do a great job ramping you to six or seven mana to start casting these bad boys
With on 65 PSA 10s its easy to see why collectors love it and are willing to pay in the thousands for it.