As little information as there is "out there" about freelancing lawyers and freelancing paralegals, information for freelancer interpreters and translators seems to be even more sparse.
From my personal experience, a large proportion of lawyers do not comprehend the delicate and critical nature of an interpreter or translator's role in legal proceedings at all. They have no understanding of the cultural impact on language and communication, resulting in inaccurate assumptions about credibility and demeanor of the foreign speaker.
I found a great article that outlines many of these problems and proposed solutions which may also be helpful to freelance interpreters as they create their marketing materials for law firms.
"A Lawyers Guide to Cross-Cultural Depositions", All Language Alliance, 2003