bargainer vs treater

bargainer and treater both are nouns.

Word	Noun	Adjective	Verb	Adverb
bargainer	Yes	No	No	No
treater	Yes	No	No	No

As nouns, treater is a hypernym of bargainer; that is, treater is a word with a broader meaning than bargainer:

bargainer: negotiator of the terms of a transaction
treater: someone who negotiates (confers with others in order to reach a settlement)

Other hypernyms of bargainer include negotiant, negotiator.

bargainer (noun)	treater (noun)
someone who purchases and maintains an inventory of goods to be sold	someone who negotiates (confers with others in order to reach a settlement)
negotiator of the terms of a transaction