I agree with Uncle Jim that this is not a good resource.BookWhirl.com:
Another way to verify your publisher is to log on to Better Business Bureau or bbb.org.
However, you can check with the Association of Authors' Representatives (in the US), Association of Authors' Agents (in the UK) or the Australian Literary Agents' Association (in Australia - obviously!) to see if an agent or agency is registered with them. These are trade bodies with criteria for membership and while it's not impossible for a rogue agent to be included, it's more likely to be a good basis for searching for reputable agencies than the BBB.