The market between firms is not really so free either. It is constrained by a myriad of government regulations related to contracts, safety, environmental protection, employee rights, information availability, international relations, etc.
In addition, anyone who has worked in a large corporation knows that there is often intense competition within the firm. Supervisors are "customers"; their staff produce new products, campaigns, rules, markets, business models for the "customer" to choose. The price signal is some mix of actual external business results, and internal power shifts. (I would guess that the mix is likely to correlate with each firm's long-term success.)
In addition, anyone who has worked in a large corporation knows that there is often intense competition within the firm. Supervisors are "customers"; their staff produce new products, campaigns, rules, markets, business models for the "customer" to choose. The price signal is some mix of actual external business results, and internal power shifts. (I would guess that the mix is likely to correlate with each firm's long-term success.)