Although the law says you owe sales tax, the reality is that gazillions of people purchase goods from another state every day and don't pay their states the sales tax the law says they are required to. So, the two questions each us answers in that situation are 1) does my conscience allows me to avoid the tax I'm legally obligated to pay, and 2) am I willing to take the risk that my state will find out and come after me.
I presume some states are more aggressiove than others in tracking down those folks owing sales tax. I sense that my state (Kansas) is not one of the more aggressive ones although I did pay sales tax even though I purchased my Kioti out of state. I did so only because I couldn't comfortably answer "yes" to both of the previous two question. I also assume states would go after a $30K sales more aggressively than a $20 online sale.
I would guess tens of thousands of folks have purchased a new tractor from out of state, opted not to pay their sales tax, yet have lived uneffected since then. To each his own.