four-flush vs sell down the river

four-flush

verb

To bluff.
To attempt to pass off a four-flush as a flush.

noun

Four cards of the same suit.

sell down the river

verb

To betray, especially in a manner which causes serious difficulty for the one betrayed.

How often have the words four-flush and sell down the river occurred in a corpus of books? (source: Google Ngram Viewer )