Such as:

• "Hey, want to buy this card for x gold? One-time offer."
• Similar for buying a card with x jewels.
• Similar for buying x jewels for y gold.
• "To assist you, I shall provide you with a [colorname] jewel."
• "I'll trade you a [random rare or mythic rare] card for [some number of copies of] [some card you own]."

More suggestions welcome.

There's already code and localization strings for "To assist you I shall provide you a [cardname] companion in your next duel." and "To assist you I shall fashion 3 [jewelnames] into a duplicate of any spell you possess." for the Wise Man screen, but I haven't ever seen them. Perhaps they're difficulty-based? The latter will have to prevent duplication of dungeon treasures per #568.