Are these valid reasons to turn down a job, and should I tell the headhunter?

I'll be saying "no" to a job offer soon. It took 4 rounds of interviews over 6 months to get the offer, and I was the finalist (since 3 months ago).

Should I just tell the headhunter "no", and not give a reason, or should I say the following?

1. At the last round of interviews, the Executive Committee told me that I should not change jobs as much as I have. One Executive Committee member also emailed on his iPhone throughout the interview, indicating that I'm not important at all to the firm.

2. It's taken 6 months for the firm to extend the offer, indicating that the new position is not particularly important to the firm.

3. Even though the salary is above what I make now, the salary is significantly below market rates.

4. If I had gotten the offer several months ago, I would have likely taken it, but since then, my current employer has reached out, without me asking, and given me significant good news about my career path there.

5. The new job has no promotion prospects, while my current job has strong promotion prospects.

6. The new job does not seem to include a way for me to generate my own clients, and in my career, not having clients is lethal to a career. (Of course I would not take my new boss's clients.)

6. The new job would entail working for just one person, which is a significant risk.

Just tell the head hunter something along the lines of "Thank you for your interest in me and submitting me for this opportunity. After considering the offer, I just don't think it's the right fit for me at this time."

Regardless of your reasons, it sounds like you are happy in your current employment situation. You don't want to burn a bridge with a head hunter, you never know, you may need them in the future. Just keep it classy, gracious and professional.

Say something simple such as a new opportunity has arisen where you currently work.