Which action exemplifies unethical practice in obtaining competitor marketing information?

Posing as a security guard to gather information is a clear demonstration of unethical practice because it involves deception and misrepresentation. This method violates ethical standards regarding honesty and integrity in business practices. Using fraudulent means to obtain sensitive information undermines trust and can have legal repercussions.

In contrast, actions like purchasing competitor data and conducting focus groups transparently can be ethical if they adhere to legal standards and industry norms. Searching websites for information is generally accepted as a standard practice in competitive analysis, as it relies on publicly available resources.