pitchman vs seller

pitchman and seller both are nouns.

Word	Noun	Adjective	Verb	Adverb
pitchman	Yes	No	No	No
seller	Yes	No	No	No

As nouns, seller is a hypernym of pitchman; that is, seller is a word with a broader meaning than pitchman:

pitchman: someone who travels about selling his wares (as on the streets or at carnivals)
seller: someone who promotes or exchanges goods or services for money

Other hypernyms of pitchman include marketer, trafficker, vender, vendor.

pitchman (noun)	seller (noun)
someone who travels about selling his wares (as on the streets or at carnivals)	someone who promotes or exchanges goods or services for money
an aggressive salesman who uses a fast line of talk to sell something