I assume that "media commission" is plain enough. The way I understand the sentence can be restated as follows:

"It is necessary to make a reasonable estimate of media commission that the agency will earn in proportion to what is required of the agency in terms of supporting all that the product assignment needs if a period of test marketing takes place."

This is not offered as a edited substitue for or as an improvement over the original sentence, but merely as a somewhat plainer, if wordier, version, to clarify the meaning.

I assume the "agency" is a company that handles the advertising/marketing of products. Each product is handled as an "assignment," and each assignment has its own requiremnts, i.e., makes certain demands on the agency to meet.

The agency earns media commissions as it handles such product assignments, and this sentence suggests that such commissions need to be estimated or "assessed" more reasonably than they are assessed now, if the product is intended to go through a period of "test marketing" .


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