Sales Tax Pile-On
You haven't heard about it yet, but you will soon enough: The Supreme Court, in a 5-4 decision, just green lighted sales taxes for Internet sales. Not just sales in your own state, but all sales!
If you sell online, this impacts you. If you sell on Etsy or Ebay, for instance, all your customers will now have to pay sales tax. In the end you may not see the change, because your online host will handle it for you. The fact of the sales tax may or may not affect sales, but chances are you won't notice.
If you run your own website, the degree of difficulty depends on the tech you use. Most e-commerce websites now use out-of-the-box solutions that handle all the dirty work for you. As long as you use one, you should be OK.
How messy can this be? Sales taxes vary according to state, according to county within the state, and according to city. Each state has its own rules but it's common for two comparable cities in a single county to have much different rates. In Clark County Nevada, for instance, the city of Boulder City charges 8.25% while Mesquite charges only 7.1%. Tracking all this would be impossible if you had to do it yourself.
It hasn't happened yet. SCOTUS gave it the go-ahead, but it hasn't gone ahead yet. The next step is in Congress' hands, but one thing they know how to do is pass taxes, so don't hold your breath.