Teresa Neilsen Hayden lays out some straightforward advice on attracting good literary agents and avoiding bad ones. She breaks agents down into four categories: good, gormless, not very helpful, and scammers. Here’s an excerpt:
Not very helpful agents have some knowledge of and connection with the industry, but what they know isn’t current, and the people who were their best connections at various houses no longer hold those positions. They tend to have one or two notable clients plus a bunch of small fry and marginal types. These agents have two virtues: they won’t deliberately cheat you, and they can get you past the “agented mss. only” barriers. It’s still a bit like marrying someone you don’t care for because at least that way you’ll get laid: the imagined benefits will rapidly pall, while the underlying discontents will only become more irritating.
(Emphasis supplied; via Boing Boing.)