Which of the following is a guideline to follow prior to the hair design service?

Checking the scalp for any diseases or disorders is a crucial guideline to follow prior to any hair design service. This step helps to ensure the health and safety of the client, as well as the stylist. It allows the stylist to identify any underlying issues that may affect the hair or scalp, and necessary precautions can be taken to avoid any complications during the service. By assessing the scalp, the stylist can also tailor their approach based on the client’s specific needs, ensuring a more successful and satisfactory outcome.

Choosing the hair color first does not prioritize the client's health or the condition of the hair and scalp, which is essential for a safe and effective service. Ensuring proper lighting is indeed important for visibility during the service, but it does not directly pertain to the health assessment of the client, which should be a fundamental step. Discussing product pricing is relevant to the business aspect of the service but does not focus on the immediate health and preparation considerations necessary before starting the design process.