I have bought farm equipment at auctions several times and never paid sales tax, I fill out an Iowa sales tax exemption form and email it to them. In December I bought a mini excavator and a few other things on an online auction. I called before paying and told them I would send them a tax exemption form. They didn't  add tax to the corral panels or fork lift fork extensions but said they had to charge tax on the mini excavator because it was construction eq. They suggested I have my tax man send in the form. My tax man doesn't seem to know what is expected. The invoice specifies "Tax1 Green County" and it amounts to a few thousand dollars. Wisconsin sales tax seems to be 5% and another .45% local tax. What do I need to do to get the tax money back? Thanks.