Except, as has been pointed out before, dealer/manufacturer financing is NOT a retail loan in the traditional sense. If you buy a car, there will be a lien filed on the title and the finance company will repossess the vehicle for non-payment. With the tractor financing agreements/sales contracts - the manufacturer does not hold a lien upon the tractor as collateral for their lending. It is pretty much an unsecured personal loan (unless you purchase the payment protection) and if you fail to pay - the only thing that will happen is they will attempt to get you to pay or send you into collections where the collection agency buys your debt and hounds you while also trashing your credit report/score.
If I financed a tractor today, took delivery tomorrow, I could sell it that day and walk away with cash and NEVER pay the finance company. They do not hold any collateral and that tractor is 'gone'. Where there is no physical presence in a state, physical retailers are not obligated to collect and remit another state's taxes for them.