Hashtags are a very powerful tool if they're used correctly but for that, a person needs to have all the important knowledge to use them in the right manner. This is exactly what the interviewer seeks to know with this question and you, to begin with, start explaining their usefulness such as how they help you identify your target audience and then help you create your niche and connect with them. You also need to explain your desired ways of using hashtags and how you intend on avoiding spam hashtags.  For example, if your business is associated with selling smartphones, you can easily connect with all the smartphone lovers, i.e., your customers and potential customers by using some hashtags identified and acknowledged by then. These hashtags help in unifying your audience.   As far as the ethics of posting goes, the interviewer hopes you know certain unsaid codes of conduct that need to be followed for running a secure and controversy-less business, which include avoiding fake claims, tarnishing someone else's image, and disclosing confidential information about your business or customers. For a social media manager, following these ethics is vital.