highway robbery vs price gouging

highway robbery

noun
  • Said of excessive or exorbitant prices. 

  • The act of robbing a traveler on a public road. 

price gouging

noun
  • The act of or an instance of charging services or pricing goods at unreasonably high prices. 

How often have the words highway robbery and price gouging occurred in a corpus of books? (source: Google Ngram Viewer )