If you buy a card via Black Market, Hermit should not trigger.
Dominion Online has fixed this, and now does it correctly.
Dominion Online apparently does not do this interaction correctly any more.
JW plays Black Market
JW reveals Secret Chamber, Spy, Embassy
JW plays Copper
JW buys Embassy
JW gains Embassy
Lord Bottington gains Silver
JW places Secret Chamber on bottom of the Black Market deck
JW places Spy on bottom of the Black Market deck
JW plays Hermit
JW trashes Estate
JW gains Fishing Village
JW trashes Hermit
JW gains Madman
JW draws Curse, Curse, Copper, Hermit, Copper
But wait, in the same game the interaction was handled correctly. Does Dominion online get the interaction correct with multiple Hermits in play, but not with only one? Or is it a random process? Stay tuned for exciting future investigations!
JW plays Hermit
JW trashes Curse
JW gains Hermit
JW plays Hermit
JW trashes Curse
JW gains Hermit
JW plays Black Market
JW reveals Remodel, Catacombs, Hunting Party
JW plays Copper
JW plays Copper
JW plays Copper
JW buys Catacombs
JW gains Catacombs
JW places Hunting Party on bottom of the Black Market deck
JW places Remodel on bottom of the Black Market deck
JW draws Worker's Village, Rats, Rats, Copper, Fishing Village