mark down vs undersell

mark down

verb
  • To reduce the price of. 

  • To write a memorandum about. 

  • To subtract marks or points from, for an error. 

  • To draw a conclusion about something; to consider something to be a certain way. (Typically used with as.) 

  • To write down. 

undersell

verb
  • To sell goods for a lower price than a competitor. 

  • To sell something for less than its value. 

  • To put forward an idea, or to market a new product, with insufficient enthusiasm. 

How often have the words mark down and undersell occurred in a corpus of books? (source: Google Ngram Viewer )