Here are a couple of examples that might help clarify the issue. Well... maybe not the second example.
Example 1:
Lets assume that the retail sale of a bag fertilizer for home use (non commercial) is taxable. A person walks into a store and purchases a bag of fertilizer and is charged sales tax. A second person walks into the store and buys the same bag of fertilizer but tells the sales clerk he/she is using the fertilizer to grow a commercial crop to be later sold. Then the clerk needs to have the purchaser fill out an exemption form because this taxable item now is exempt from sales tax because it is going to be used for a commercial purpose. (This is the current tax law for fertilizer in Vermont)
If all fertilizer was tax exempt then no one would have to fill out an exemption form because all sales would be tax exempt. (This used to be the tax law in Vermont)
The new fertilizer tax law in Vermont makes it much more difficult to charge/pay the correct sales tax on fertilizer in Vermont.
Example 2.
This one shows the potential conflict with origin based sales tax vs. destination based sales tax.
Origin based sales tax =
a system where sales tax rates are determined based on the location of the seller, not the buyer.
Destination based sales tax =
the tax is applied based on the location where the buyer takes possession of the item or where it is delivered.
Example 2: Customer walks into a flower shop in Newark, California and want to send $100. of flowers to someone in Stowe, Vermont. California is an Origin based sales tax state and the paying customer is in California so it would be logical to conclude the sales clerk should charge California state sales tax, as well as any county and city taxes that might apply (google says this is 10.75% total). But wait, the flowers are being delivered to Vermont, a destination based sales tax state (this is where the item is delivered). According to Vermont law, 6% sales tax is due to Vermont. The town of Stowe also has a 1% town sales tax so that must be added to the total as well. Lets assume for a moment this is a smart sales clerk and he/she knows all of this or the point of sale software calculates this and the customer looks at the receipt and sees the 17.75% they were just charged for sales tax and says, wait a minute, you cannot charge me sales tax twice on the same item for one sale!
Houston we have a problem! I have talked to a lot of people (much smarter than I) from around the country about this and, to date, not one person has been able to explain how to satisfy all parties involved in this scenario. The Vermont Department of Taxes claims this sale doe not take place in California despite the fact that the customer is standing in the flower shop in California and is the one handing over the money. I would expect the California Department of Taxes would not agree with Vermont's position on this, but I have not personally asked them.
Bottom line is, sales tax is a huge can of worms. You just have to try to do your best, but sometimes it appears to be impossible to get is right.