I kinda feel the card is too wonky. At its worst, this card is a worse Pawn, as ThetaSigma12 said. At its best, it's completely bonkers. Even if it turned the buy only into one of the bonuses (amd gave the other as a baseline) as Classic_Rush suggests, which do you pick? Markets become super-Labs with the Cards and only Bazaars with Actions, whereas Margraves become Super-Duper-Labs with Actions and Hunting Grounds with Cards. As much as I dislike Storyteller, I still feel that card implements the concept of turning one resource into another better, simply because of the exchange rate of coins and cards, and the non-issue of losing all your coins compared to losing all your buys.
Perhaps a Crossroads wording that can only exchange one buy per turn would allow you to make the base version stronger without it becoming crazy overall. Maybe a +1 Buy cantrip that can instead lose a buy the first time to be a Lost City?
Fiddler
+1 Card
+1 Action
Choose one:
+1 Buy; or
If this is the first time you played a Fiddler this turn, lose one buy and +1 Card, +1 Action.