Which of the following is a ground for disciplinary action against an esthetician?

Failure to display a license is a ground for disciplinary action because it violates the regulations that require licensed estheticians to visibly display their credentials in their place of work. A visible license ensures that clients are aware of the professional qualifications of the esthetician they are receiving services from. If a client cannot see the license, it may lead to questions about the legitimacy and qualifications of the practitioner, undermining consumer trust in the profession. This requirement promotes accountability and helps maintain standards within esthetics.

While the other options represent serious violations that could also warrant disciplinary actions, the emphasis on failing to display a license highlights the importance of transparency in professional practice. Display of credentials is a fundamental aspect of ensuring that clients are informed and can make educated choices about the services they receive.