system
Given the following post, respond as if you're commenting on Reddit:
human
How does a consultant actually find a firm's profit-maximizing price and quantity in practice?

In a microeconomics course, students are given "supposed" marginal cost and marginal revenue functions so they can solve for the profit-maximizing price and quantity.  In the real world, these functions must be found with real empirically data.

Suppose a consultant is trying to inform an entreprenier/investor on what price and quantity he should charge for his new business he wants to open up in a few months.  How does the consultant go about predicting what this firm's marginal cost and marginal revenue functions will be?
gpt
Real world prices are not related to the theories of marginal cost and marginal revenue - this is very well documented and widely understood. These theories require conditions which do not hold in practice. For an example of a high quality survey that confirms this, see Alan Blinder's *Asking About Prices*. 

Firm's typically set prices based on a markup over cost and use trial and error to determine (maximum) profit margins. That said, it depends on the industry, e.g., there are many industries which are "price takers" and therefore suppliers get the price they can get and do not "administer prices" with a profit markup over cost. There are also industries where prices are set by auction.