We usually emphasize the producer (or the supply side) of pure competition.

What if we have many producers of a homogenous product but only a few buyers or one or two input suppliers.

Many farmers feel they are in this situation. There may be only three possible buyers for their cattle. There are only a few places they can buy some inputs such as fertilizer. Or, at least, there are only a few companies that produce the fertilizer. They feel they are pure competitors but their buyers and suppliers are not.