When facilitating the purchase or sale of securities in the open market for a customer...

A firm acts as a broker when it facilitates a securities transaction for a customer as agent and charges a commission. In agency capacity, the firm does not buy from or sell to the customer out of its own inventory; it helps execute the transaction in the market. Choice B is correct. A dealer acts as principal, meaning the firm buys or sells securities for its own account and typically earns a markup or markdown rather than a commission. Choice C is therefore the opposite capacity from the one described. A transfer agent maintains issuer shareholder records, cancels and issues certificates, and processes ownership changes; it does not act as the executing firm charging commissions for open-market customer trades. The SIE outline specifically includes “Trade capacity,” with examples of “principal” and “agency,” and identifies broker-dealers as market participants. This is a core market-structure distinction: broker equals agent/commission; dealer equals principal/markup or markdown. Reference: Section 1.1.4 Market Participants and Their Roles; Section 3.1.1 Orders and Strategies, trade capacity.