The market failure that observes when a cost or benefit is not reflected in the price of a good is

Externality

Explanation:

An externality is an economic term that refers to an expense or profit that a third party has paid or earned.

The third party, though, has no influence over the expense or benefit being created.

The externality can be either positive or negative and can arise from either a good or a service being generated or consumed.

The costs and benefits can be either personal — to a person or an entity — or public, which means it can influence the whole of society.

answer; intensive use of a sales force and is relatively costly;