cosmetician vs seller

cosmetician and seller both are nouns.

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

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

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

cosmetician (noun)	seller (noun)
someone who sells or applies cosmetics	someone who promotes or exchanges goods or services for money
someone who works in a beauty parlor