Another way to verify your publisher is to log on to Better Business Bureau or bbb.org.
I agree with Uncle Jim that this is not a good resource.
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.