Earlier quoted context omitted.
I don't think that becoming dependent on a particular product, service, or supplier makes it "not a free market."
http://en.wikipedia.org/wiki/Free_market#Overview Adam Smith believed that an economy should be free of monopoly rents If I can keep you from switching lawyers, if I can keep you from interviewing other lawyers, if I know your choice is not "lawyer or no lawyer", but "which lawyer", then I can keep my prices artificially (not a free market) high.
What this means is that theoretically a large, valuable client can negotiate a multi-year cap on rates or rate increases, etc., which then operates as a multi-year option contract. The client can always choose to switch firms anyway, but also has the value of knowing in advance that the rates at its current firm will go no higher than X in year two or Y in year three.