The idea that is not consistent with perfect competition is product differentiation.
A perfect competition is a market where there are many buyers and sellers of identical goods and services. Market prices are set by the forces of demand and supply. This, they are price takers. There are no barriers to entry or exit of firms into the industry.
Here are the opti0ns to this question:
product differentiation
freedom of entry or exit for firms
a large number of buyers and sellers
price-taking behavior
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