Can I tell them I'm not interested? (Decline Job Offer)
It's perfectly acceptable to say, "Thanks, but no thanks".
Remember that even if this particular opportunity isn't fitting at this time, remaining professional, gracious and kind will serve you well. Each interview opens the door for us to grow our network. You never know who the hiring manager/interviewer knows, what other opportunities they are aware of or who they might mention your name to in passing.
So first, thank them for their time and consideration. Although interviewing/hiring is part of their job, chances are, they spent a lot of time reading your resume and documentation, as well as researching your social media - so a heartfelt thank-you will go a long way:
"Thank you so much for the offer for the Marketing Manager position. I so appreciate you taking the time to consider me and for addressing so many of my questions about the company and role."
"Thank you again for the interview last Wednesday, it was great to meet the team and see the offices. I enjoyed learning about the Operations Director position, and I appreciate this generous offer."
Then provide a brief explanation about your specific reason for not accepting the position:
After careful consideration, I’ve decided to accept a position at another company.
After much thought, I’ve decided that now is not the best time to leave my current position.
While this position seems like a great opportunity, I have decided to pursue another role that will offer me more opportunities to pursue my interests in marketing and social media.
Finally, offer a small pleasantry before signing off. Keep in mind that in certain industries, the circles can run small - make sure if you're mentioned, a positive thought comes to mind.
If you can reference something you discussed, like an event or conference you’re both attending, do so. Otherwise, you can make a simple mention that you wish this person all the best in the future.
I hope to see you next month at the conference we’re both attending.
It’s been a pleasure getting to know you, and I hope that we cross paths in the future.
Again, thank you for your time and support, and I wish you all the best.