Buying a used RV in Arizona from Out of State

[ph007]

My friend is looking to buy a used RV from a Dealership in Arizona. He lives in Michigan where it will be registered. The dealership wants him to pay sales tax there which includes Local and City taxes. Told he will also had to have title transferred down in Arizona.When he gets back to Michigan he will have to have it transferred again. As for the tax they said they will collect it and send it to Michigan as their tax is lower and he will only have to pay the difference. All together $5000 on a $55000 deal. I'm afraid when he gets to MI he will have to pay again. So I called the AZ DMV and they said all he needs is a drive off permit which is $15 for 30 days and can pay the taxes when registered in MI. As anyone done any buying from a dealership in AZ from out of state. Smells fishy to me.