There's no way currently to sell items in the game. However, there is a cheat option that clears the inventory, and another cheat that lets you add any item, so there's that.
To get the pickle potion, keep exploring the alleyways, it is there. (And once you got it, you can use it from your inventory.)
I second the suggestion that Kazuma should try to hit on girl adventurers, and get in trouble for it. Would be in character.