Preventing Form Spam
There are many different techniques for preventing form spam on your website, and an important component of the battle against spam is your constant struggle between giving your 'real' users a good experience while preventing spammers and automated bots from spamming you and lowering the quality of the content on your website.
A Constant User-Experience Battle
Usually, the first thing someone will do after having trouble fighting spammers by manual comment/content moderation is place a complex CAPTCHA system on their forms. Something like this: