Spammer verification

[goodhunting1]

The way we have our board set up with Q&A to get in. You have to email the admin account to get the response. At that time all I have is an email account. I would go to http://www.stopforumspam.com/search and check that email. If i dont get any hits and the person seems legit then I send them the answer. Once the person register they will have to wait for moderation, IF I see a bunch of other people registering at the same time I know the answer has been compromised and has to be changed, then delete all those users waiting for moderation. IF I only see that initial person then I can use the same website to check the ip. Are there other resources to help with spammer verification?
This website is small, just a bunch of guys and pretty much membership is by invitation (we do allow and welcome new unfamiliar users) so doing all this manually is not a big task.

Thanks!