customer vs sitting tenant

customer

noun
  • A patron, a client; one who purchases or receives a product or service from a business or merchant, or intends to do so. 

  • A native official who exacted customs duties. 

  • A person, especially one engaging in some sort of interaction with others. 

sitting tenant

noun
  • A tenant who is already in occupation of a premises, especially when there is a change of owner. The tenant is not evicted when the property is sold to a new owner. 

How often have the words customer and sitting tenant occurred in a corpus of books? (source: Google Ngram Viewer )