Too Much Marketing?

In the wake of my attendance at the tekom conference late last year and as part of my New Year's resolutions, I've sent out quite a bit of marketing material lately. Now I seem to be finally reaping the benefits, in the form of translation projects. That's what I was aiming for, so that's good, right?

Well ... I did want to generate more business in the form of projects being offered. But now I find myself in the (some would say enviable) position of having to turn projects down because there are too many coming in at once. That state of affairs is, of course, fairly common to the freelancer's life and has happened in the past, as well. I have always made good on my promise of quality delivery on time and therefore won't take on more projects than I can successfully handle.

The difference is this: established clients understand that sometimes I have too much work and will need to turn them down. Occasionally they will even postpone a deadline and wait for me to catch up on on my workload. While new clients understand this, too, in principle, if I turn them down more than once, they'll wonder why I bothered marketing to them in the first place and stop offering me projects. Then the draught of work will set in and I will start marketing more, and ...

So how do I know when I have enough potential clients in the pipeline and should stop trying to acquire more? Frankly, I don't know how to determine that. Are there any rules of thumb? Do you have any experience with this? Your input is appreciated.