:: a guide to reject clients ::

I thought this will happen one day on a magical graphic designer heaven when I'm the best designer in the world and everybody will want me to do creative projects for them. But today I have to face the hardest part of my job so far: rejecting a client (politely, of course). There should be a guide out there on how to strategically decline a client whose project is just too impossible to be done, either the timing's not right or the clients themselves are not accomodating in many ways. How to do this, people? It's not that I'm so proud I won't take small projects, it's just that the timing really wasn't right. However if I told this to a client, doesn't it sound a bit unprofessional? Shouldn't a good designer is able to do anything anytime with a limited resources? Anyhow I feel so guilty afterward, because I know that if I forced myself, I should've been able to do it, although maybe not as good as it could have been if I spend a little more time with the project. I do hope somebody will write a guide on the appropriate ways to do this. Please?