Answer: They should not.
Step-by-step explanation:
When it comes to the advertising industry, the wishes of the client are not of the highest priority, they are of the second highest priority.
The highest priority is to the industry and its integrity. If advertisers acted in an unethical manner, they would risk destroying the reputation of the advertising industry which would lead to a massive loss of trust in it that could severely impact it.
Regardless of how important a client might be therefore, their wishes should never trump the ethics required in the industry because these ethics maintain the integrity of the advertising profession.