"Sold down the river" is an idiom meaning betrayal or deception—especially by someone trusted. It does not imply literal sale or river transport.
Rooted in US slavery: enslaved people in the Upper South (Virginia, Kentucky) were "sold down the river" to harsher Deep South plantations (Mississippi, Louisiana) via the Ohio/Mississippi Rivers. This meant separation from family, brutal conditions, and often death.
The idiom describes the victim's experience, not the betrayer's fate. Outcomes vary:
The phrase condemns the act, not a predetermined punishment.