If you are purchasing materials that will be resold, or used to build a product that will be sold, you do not need to pay tax on those materials. It's a simple matter to get a sales tax certificate from your state -- you can do this online in many states. When you buy the materials, you give the seller your sales tax ID number and that will remove his need to collect the tax from you and your need to pay it.
So if either of you are audited, he can point to your ID number as the reason he didn't collect and pay tax and you had better be able to show that you collected and paid tax from the people you sold your product to.
If you are purchasing materials that will be resold, or used to build a product that will be sold, you do not need to pay tax on those materials. It's a simple matter to get a sales tax certificate from your state -- you can do this online in many states. When you buy the materials, you give the seller your sales tax ID number and that will remove his need to collect the tax from you and your need to pay it.
So if either of you are audited, he can point to your ID number as the reason he didn't collect and pay tax and you had better be able to show that you collected and paid tax from the people you sold your product to.