Contact form spam

Hi,
My client got the same email sent from his website contact form about 5 times in the last 10 days from the same marketer trying to promote his services. Is there any way to stop this?
(not sure if I should respond - or try another tactic)

I have a new website, which i created and added the cleantalk plugin, It really works, the clients is not complaining about spam - but what actually got me wondering is that on the weekly report i see quite a few attacks and this is on a new site.