buyers' market vs marketplace

buyers' market and marketplace both are nouns.

Word	Noun	Adjective	Verb	Adverb
buyers' market	Yes	No	No	No
marketplace	Yes	No	No	No

As nouns, marketplace is a hypernym of buyers' market; that is, marketplace is a word with a broader meaning than buyers' market:

buyers' market: a market in which more people want to sell than want to buy
marketplace: the world of commercial activity where goods and services are bought and sold

Other hypernyms of buyers' market include market, market place.

buyers' market (noun)	marketplace (noun)
a market in which more people want to sell than want to buy	the world of commercial activity where goods and services are bought and sold
	an area in a town where a public mercantile establishment is set up