There certainly exist Black Market strategies; Black Market/Tactician being a good example.
This is what I was going to say, too. Some cards just take on a whole different character with the Black Market. Tournament and Tactician are good, but consider some other cases. There was an "in-person" game I played recently where there were both a Remake and an Upgrade in the Black Market when there was no trasher in the primary set of 10. I got both. Guess who won?
Also, consider a card like the Trade Route. If you're the only one with the Trade Route, you don't have to worry about the caveat of extra victory cards purchased causing other players to gain the bonus as well. Possession also comes to mind. It is certainly difficult to purchase with a Black Market deck, but if you do, your opponent can't counter by also obtaining one. They probably also haven't prepared for it as well.
Conversely, there are not some cards that perform as well in the Black Market. The Young Witch is a good example, especially if there are other curse givers. Theory also pointed out some of the downsides to having Tournament in there; by that point, a Prize may not be as advantageous.
This can apply to practically any card with a major attribute that is not present in the normal set of 10.