I suppose the real question is is the dealer charging Michigan tax AND 50% MO tax?
On the west coast, no sales tax in OR. If you buy in OR you have to pay the tax from where you live on large purchases. My concern would be if you paid MI tax and 50% MO tax, what would you be charged when you register the veh. in MO. Shouldn't have to pay double tax.
Also, in WA they ask for your zip and charge that tax. WA pays as much if not more than CA so it doesn't really matter.
I believe most states charge your home state tax, but am not sure.