Navigating the labyrinth of career decisions can be daunting, even for those with the most impressive of academic qualifications. Even the brightest Harvard graduate may find the career landscape a tough terrain to traverse. Enter career counseling services, a compass guiding you through the muddled pathways of career options. But how do you ensure the service you engage is up to the task? There are six critical questions you need to pose to your prospective career counseling service provider to establish their credibility and efficacy.

First, inquire about their credentials. The career counseling field, although intricate, does not have a defined, clear-cut qualification pathway. It is crucial to ascertain if your prospective counselor has a background in psychology or a related discipline, as this provides an understanding of personality theory, assessment, and counseling techniques. In addition, certification from recognized bodies such as the National Career Development Association (NCDA) or completion of respected courses in career counseling adds to their credibility.

Second, delve into the methodology they employ. Career counseling is not a one-size-fits-all service. A counselor must engage a client-focused and tailored approach, utilizing a blend of psychometric assessments, interviews, and counseling sessions. Renowned theories by Holland, Super or Krumboltz might be utilized, but the counselor must explain their rationale for choosing a particular model and how it aligns with your circumstances.

Third, it would be prudent to address the frequency and nature of sessions. Are they one-off, or is there a structured plan? Does it include follow-ups? In career counseling, continuity is key. Regular interactions help the counselor understand your personality better and facilitate more accurate advice.

Fourth, investigate how they stay up-to-date with the labor market dynamics. The employment sector is a rapidly evolving beast, and your counselor must demonstrate their commitment to staying abreast of trends, new industries, and job roles emerging. This ensures that their advice is contemporary, practical, and relevant.

Fifth, ask about their success stories and case studies. A reputable career counseling service should provide evidence of their effectiveness. Don't shy away from asking for anonymized case studies or success metrics. This can give you a benchmark to understand what to expect and how they can support your career journey.

Lastly, address the elephant in the room - cost. While it’s vital to invest in professional guidance, make sure you understand the fee structure, payment terms and if it's congruent with the services offered.

Drawing upon the Nash Equilibrium, a solution concept of a non-cooperative game involving two or more players, we can understand that career decisions are essentially a strategic scenario, where the 'player' (you) is trying to make the best choice considering the strategies of others in the labor market. The 'payoff' is the success of your career. Your counselor is essentially your coach, helping you make those strategic decisions.

By asking these paramount questions, you place yourself in a position of informed power. It allows you to sift through the noise and engage a career counseling service that is transparent, professional, and best suited to your needs. Remember, this is an investment in your future, and due diligence is the foundation on which you build a successful career.

In conclusion, to paraphrase Sun Tzu's Art of War, "Every battle is won before it's fought." Career decisions are your battles, and a competent career counseling service can equip you with the right strategy to win. Understanding your counselor's qualifications, methodology, frequency of sessions, relationship with labor market trends, success stories, and cost structure will empower you to make an informed decision, leading you closer to your ultimate career victory.