Most writers know first hand to research everything they do either because of their own personal experiences or the words of another who had not been so lucky.
Writers.net and Absolutewrite.com are the ideal spot for writers of any genre, fiction or non-fiction to get together and talk. Their forums are full and helpful, and because of the sheer number of members you can usually expect several answers to your questions within the hour.
Writers.net divides their forums the way most would expect, by topic of published authors, unpublished authors, literary agents, and just plain discussing your writing. Absolutewrite is mostly the same, but their site is much larger, has a detailed list of how publishing works, grammar, what to expect from a legitimate and a fraudulent agent, and includes a list of the 20 worst agents can be found on their Bewares and Background Check area in the Conference Room of the forums.
Before any writer submits a query letter they should always check in on either of these two websites (preferably both) to ask other members of their experiences with the agent or publisher they are submitting to. One topic that is constantly brought up would be the ongoing scam with the New York Literary Agency (Which appears on the list of worst agents) and Publish America, and the warnings for all authors to stay away. As some people already know (and if you did not know then you should try it just to see for yourself), if you type Literary Agents into Google, The New York Literary Agency is the first on the list to appear since it is a paid advertisement. Questions have been raised as to how to send Google a complaint for this, but so far nothing has been done to remove it.
Members are generally very friendly, welcoming and helpful. I would recommend any of these websites for any new writer or old writer looking for advice or help.