Captcha or AreYouHuman would help against bots posting to the helpdesk, but I have had instances where "a human" would submit a "SEO offer" (every other day), got annoying real fast.
If you could ban email addresses/domains/IP it would cut down on this type.
Even had a hosting/domain firm offer me a domain reseller account at "fantastic prices", yeh right, the prices they offered me to buy domains from them was higher than what I was selling them for on my site. /fail