Sentence:  The idea of a merchant selling both totems of pure evil and frozen yogurt (he calls it frogurt!) is amusing in itself, as is the idea that frogurt could be cursed, but it's really the Shopkeeper's quicksilver shift from ominous doomsaying to chipper <WSD>salesmanship</WSD> that sells the sequence. 
Meaning of the word marked with <WSD> tags:  The skills and knowledge of how to sell.