When you say you have checked with Google there is no fraud involved, what exactly have they said they have checked? The only way I could see of evaluating if the forms were the result of fraud would be checking they didn't come from the same IP address (similar to how they try to identify 'click fraud') but this is fairly easy to mask with an extension like Stealthy or a more sophisticated IP masking app. Few Qusetions -
Could you give an example of how the info is 'fake' ie legitimate sounding inquiries with a fake email address or is it just nonsense information?
Do the forms look like they may have been spammed by some sort of bot or automated program? Usually relatively to spot this kind of thing ie repetiton of some sort of pattern or syntax that would never be entered by a human etc.
Has your client recently (or ever) had an acrimonious situation with a competitor or past client/customer?
My first suspicion would be someone (most likely a competitor) taking 'click fraud' to the next level by also wasting staff time with dodgy inquiry forms, a little elaborate but really the only logical conclusion I can reach. I would also say this scenario is more likely in a market where cost per click is reasonably high (say £2+). Be interested to see if you discover any more.
Oh, one more thought having said that - has a developer thoroughly checked the functionality of the form? I'm sure they checked the obvious but you never know.