Insisting that all buyers pay the same prices would yield some highly unpleasant results. Price discrimination occurs in all sorts of regulated markets. Health care providers charge myriad prices for the same services, depending on whether you're Medicare, Medicaid, indigent, privately insured, etc. Telephone companies charge different rates to business and residential customers. New York City has several different kinds of taxis, each of which has a different pricing scheme.
Scalpers raise some interesting issues.
Scalpers often appear because laws restrict the amount that sellers can charge for tickets. I believe this was true in New York City for Broadway theaters. The idea, ostensibly, was to keep ticket prices low so that more people could afford to attend. But legally mandated box office price limits carry unintended consequences. They lessen theater revenues, making it harder to turn a profit and remain in business.