1
general::
Phrase(s): sell someone down the river
Go to sell someone out.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Betray, as in They kept the merger a secret until the last minute, so the employees who were laid off felt they'd been sold down the river. This expression, dating from the mid-1800s, alludes to slaves being sold down the Mississippi River to work as laborers on cotton plantations. Its figurative use dates from the late 1800s.
American Heritage Idioms