In this moment, he's a villain. Think of him like a snake in the way you're talking. This is like a back ally deal, poor young jack has not made it to the market yet. When you're saying these lines your chest is not puffed up like a hero, your back is hunched over like a guy selling Rolexes from the inside of his trench coat.

The stranger is a man in his 60s to 70s with a playful, sly, and slightly mysterious tone. He is persuasive and mischievous, with a voice that hints at charm and intrigue to entice Jack into trading for the magic beans.
Not married to him being American or English, I can even see him being Eastern European or Arabic/ North African.