Jessica Hische, a tremendous print designer and illustrator has a section on her website titled "Why you should not hire me to design your website."  Some excerpts:

I might seem like a jack of all trades because I do print design, typedesign, lettering, and illustration, but really I’m a specialist. Ispecialize in drawing type and illustration. This is what I’m best atand is probably why you found my website in the first place. I find itstrange that I get so many requests for web design—I went to school forgraphic design, yes, but each subfield of graphic design has its ownset of problems, limitations, and guidelines.

Just as you wouldn’t expect any random person thatowns Adobe illustrator to be able to draw a decorative initial fromscratch, you can’t expect any print designer to be able to really andtruly design for web. Web design is not print design, it is so muchmore complex. With book design, a person that encounters your bookknows how to view it. They look at the cover, they open the cover, andpage by page they work their way to the end. With web design, it’s (forthe most part) not linear. You have to understand how people are goingto use the site (and how people use the web changes all the time).

Anyway, to conclude a fairly long rant: Hire people that are best atwhat they do. It’s not that I (or other print designers) CAN’T do webdesign, its that you should want to hire someone that will do itbest—someone that knows the ins and outs of the web and can then hirepeople like me to do what they do best: draw ornaments, logos,illustrations etc that will make the site sing.

I'm quite certain many lawyers and firms would benefit from a similar "disclaimer" telling potential clients why not to hire them.  Communicating what you do -- and most importantly, what you don't (and won't) do -- goes a long way towards getting you the clients you want and dissuading the ones you don't from picking up the phone.