I wrote this as a comment on another website and decided to share it here as well. This is common sense stuff, but it bears repeating.
You've finished your first novel -- congratulations! Now your work is really going to begin. Finding a good agent or publisher is a challenge, so you have to be both smart and persistent. (And lucky wouldn't hurt either.)
Do your research. Find out everything you can about someone before you do business with them. Ask questions. Who else does the agent represent? Who else does the publisher publish? Are their books available at bookstores? Do they get reviewed?
These days, anyone with a credit card can call themselves a publishers. Most of them are nothing but con men.
Always remember: publishers pay you -- not the other way around. If anyone (editor, agent, publisher) asks you for money, run in the opposite direction.
This is a tough business and getting tougher all the time, which means the opportunities for the crooks will only increase. Don't let yourself be taken advantage of.