You will probably need to get a dealer’s license. This is no big deal. See the Michigan Dep’t of LARA Building Codes division etc.
You will need to withhold and forward to SOS the sales tax of 6% on the sales price.
If you don’t have the actual physical title from DMV/SOS I think you will need to get certificate of title, sign over to new person, and take certificate of title to DMV/SOS for updating their ownership records. You may be able to do some of this by affidavit & “bill of sale.”
If you want to sell on credit (time), you are opening a whole other can of worms.