Property Tax Protest

With property tax valuations out I was wondering what advise anyone could provide on how to best fight the appraisal. The appraiser is using unverified information from loopnet to support the assessment. We purchased the property at the end of 2008. They said they also look at the income approach. I am wondering if anyone has had success either DIY or with one of the tax consultants. The proposed increase would increase our tax liability by 40k per year.

Thank You