exchange of contracts vs quid pro quo

exchange of contracts

noun
  • The act of exchanging contracts. 

  • The point or stage at which a conveyancing contract comes into existence between negotiating parties for the carrying out of a disposition of an estate in land; usually requiring the payment of a deposit. 

quid pro quo

noun
  • An equal or fair transaction or series of process of exchange transactions; tit for tat. 

  • Something which is offered or asked for in exchange for something else. 

  • Something which is understood as something else; an equivocation. 

  • Substitution of one drug for another. 

  • A usually non-monetary exchange transaction, or series or process of exchange transactions. 

  • Sexual harassment in which a person in a workplace implicitly or explicitly requires sexual favours in exchange for something. 

How often have the words exchange of contracts and quid pro quo occurred in a corpus of books? (source: Google Ngram Viewer )