Sometimes, someone comes to you with a job, project, or idea that – whatever its quality – you either can’t get excited about or don’t have time to assist with. If the person presenting this to you is a friend, co-worker, or similar connection, you are stuck in the difficult position of having to let them down easy. Even if it’s someone you don’t know or feel strongly about, it is important that you treat him or her with respect. You never know who will be famous, rich, or a friend down the line and ruling people out or treating them poorly is never a good idea.
First, you should address to yourself why you are turning this offer down. Is it about the money, the project itself, the person presenting it to you, or your own time limitations or capabilities? Knowing yourself and your limits is important and being honest with yourself first will help you to come up with an appropriate answer.
In communicating with the person contacting you, do not leap to a quick, “No.” Think over the situation and what you can do to be valuable despite your rejection. If you like the project but cannot do it yourself because of time, you might be able to recommend someone who can commit. If it’s about money, perhaps you know a capable younger person looking for a start that can take a lower salary. If you can help to find someone else to fill the position, that can be as good as taking it yourself and, if things work out, will reflect well on you with both parties.
However, if your doubts are about the person captaining the project or the project itself, you don’t want to pass them along to any of your friends or connections. Depending on your relationship with the person, you can very gently and subtly suggest some changes without burning bridges or being rude.
That said, in those cases it is often best to make your excuses and a quick exit. Find a valid and perfectly understandable reason (preferably that’s at least mostly true) and bow out.