Lawyers are perfectly well aware that a) if they try to screw you, another lawyer will happily screw them right back on your behalf and b) their social position is precarious enough as it is; no jury would convict an anti-lawyer lynch mob.
Unfortunately, this is a legitimate concern. You can't really sue someone for giving you subpar legal advice. It has to be really, really bad. And you would be surprised at how rare it is for a lawyer to lose a malpractice case. Doctors, sure, lawyers, not so much. It turns out that juries actually respect the work lawyers do when you get them in a courtroom.
On the plus side, if you really do get screwed, a lot of states have funds set up to compensate you. But if you pay for some legal work that might not have been completely necessary, you're on your own.
I don't think lawyers are inclined to go after their bretheren this way, but I do think lawyers get a lot of business through referrals, and clients who don't feel like they've been screwed will refer friends and colleagues.
This would be particularly important in corporate law for small businesses, where the lawyers have ongoing relationships with clients (as opposed to, say, personal injury law, where some guy hit by a truck picks an attorney out of the Yellow Pages and may never deal with the lawyer after that case is resolved).
Of course, I'm making suppositions based on my knowledge of economics. Maybe I should consult an economist.
