What is the difference between a tax exemption form and the tax exemption certificate?

I help my dad out in his mulch business I do the receipts n today a customer came in n complained about me.charging him tax. I told him he needed the tax exemption certificate in order for me not to charge him tax. He complained and said I was suppose ti have forms for him to fill out so he wouldnt have to pay me the taxes because when he does his taxes they'll charge him taxes again. So I called a notary to ask if I had to provide such form she said no that they had to show me the exemption certificate. And the guy came back and I told him.what I was told then he complained and called me a liar. And said that at other mulch business and nursery's they offered those forms and that it wasnt a tax except certificate that it was a form and that you didnt have to get it notarized that if you went to the county tax office they gave you a whole stack of those forms soo