A shyster (possibly derived from the German Scheißer, "shitter"[1]) is an individual who tends to be flexible with his choice of words and sensitive to the sensibilities of his audience when he discusses fiscally pertinent topics.
Translation: a shyster is accustomed to excrete torrents of bullshit over the heads of suckers, who then reward the shyster by handing over enormous wads of cash for 'safe' keeping.
A large number of ministers of religion fall into this category, particularly cult leaders and televangelists. This category also includes such creationists as are not completely insane, but are merely shilling for pseudoscience.
Extremist politicians, such as those in the right wing of today's Republican Party, or the CPUSA (especially pre-1956), as well as politicians who pander to extremists, are often shysters; for example, Ronald Reagan announced his sympathy with creationism to win over the fundamentalist voters, and promptly got elected, later being rewarded with canonization.
The term is also sometimes applied to certain trial lawyers, particularly of the ambulance-chasing variety.