"Those who prefer their English sloppy have only themselves to thank if the advertisement writer uses his mastery of the vocabulary and syntax to mislead their weak minds"

This quote by Dorothy L. Sayers is a warning to those who do not make the effort to find out appropriate English. She is suggesting that if someone does not make the effort to find out the language, they are most likely to be deceived by advertisement writers who have a proficiency of the language. She is implying that if someone does not comprehend the language, they are more likely to be benefited from by those who do. She is likewise suggesting that it is the obligation of the individual to discover the language in order to protect themselves from being misled. In conclusion, this quote is a reminder to put in the time to learn correct English in order to secure oneself from being taken advantage of.