Peeta will try to track down the kids claiming to have seen the mermaid and ask them to show him where she came from and tell him what they saw, etc, taking the whole claim very seriously.

He'll also try to find some traders from Lekk to ask them why they don't like talking about where their village is and if they would like the Heroes to visit it or not. (He uses the term 'Heroes' likes the Games uses 'Tributes,' figuring that's just what they're called.)

If he ever overhears traders and/or Astorians speaking ill of witches, he'll step in to try to reassure them of their efforts to balance.