dog-eat-dog

When the market for a good or service is ruthlessly competitive.

Investopedia Says:
Electronics retail is often thought to be a dog eat dog market. Blockbuster sales every weekend, bashing competitor products, and "lowest price guaranteed" tactics are characteristics of dog eat dog competition.

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Ruthless acquisition or competition, as in With shrinking markets, it's dog eat dog for every company in this field. This contradicts a Latin proverb which maintains that dog does not eat dog, first recorded in English in 1543. Nevertheless, by 1732 it was put as "Dogs are hard drove when they eat dogs" (Thomas Fuller, Gnomologia).