Thanks to a small team and a lot of publicity SEOmoz turns away a significant amount of work - sending folks to specific references or our recommended list or occassionally recommending they hire in-house SEO help. We're lucky in that we get to picky about the folks we choose to work with - some of the reasons for turning away business can include:
Obvious factors like:
Size of the company/project/budget
Industry focus
Competitiveness of Niche Compared to Potential Profitability
Conflicts with existing or past contracts/non-competes
And some less mainstream ones:
Quality of Linkbait Opportunities (since this has become a primary technique for us we tend to choose clients that can use it effectively)
Background of the Company or Principal Executives (this most often applies to folks seeking reputation management campaigns)
Personality match or conflict with the primary contacts
I wondered if other companies do this too so I've put together a quick poll. If you provide search marketing services (or business services of any kind) I'd love to get your (anonymous) feedback. Note that I removed a few from the above as I felt everyone turns away business based on size/price and competitiveness vs. potential (note that multiple choices are allowed):
I'd love to discuss this more as its a fascinating topic to me - client selection seems to be both an art and a science and I'm not sure if it's something we've always done a good job with... How about you?