During a registration workshop, the instructor adds this setup first. Assume the administrator is testing the cleanest state-law answer. Agent Robert guarantees a new client that her $100,000 investment will grow to at least $150,000 within one year. When the account loses value, the client sues. Which prohibited practice has Robert committed?

Why C — Guaranteeing a customer against loss in a securities transaction

Under USA Section 502 and NASAA model rules, guaranteeing a customer against loss or guaranteeing a specific return on a securities investment is a prohibited practice. Securities investments inherently carry risk, and no agent may promise a guaranteed outcome. Robert's promise of growth to $150,000 constitutes a prohibited guarantee. The governing USA principle is unchanged even though the framing is different.