I've done that quite a few times in both of my shops. I think you did the right thing. But, you are right, it is so hard to say no sometimes. Both because you wonder whether you just missed a great opportunity, and because you don't want to make the buyer feel bad. I've seen shops who have bitten off more than they could chew, end up getting really behind, not being able to deliver, getting terrible feedback, and eventually getting shut down. Much better to feel a little bit uncomfortable saying no, than to go down that road. Maybe next time it will be the right time, and you'll be able to say yes :) But the no's do get easier the more you have to do it.