Mich. Comp. Laws § 205.821

Sec. 21. A seller registered under the agreement may select 1 of the following models for purposes of collecting and remitting sales and use taxes under the agreement: (a) Model 1. The seller uses a certified service provider to act as the seller's agent to perform all of the seller's sales and use tax collection functions other than the seller's obligation to remit sales or use tax on its own purchases. (b) Model 2. The seller uses a certified automated system to perform part of the seller's sales and use tax collection functions, but the seller retains responsibility for remitting the tax. (c) Model 3. The seller has sales in at least 5 member states, has total annual sales of $500,000,000.00 or more, has a proprietary system that calculates the amount of tax due in each taxing jurisdiction, and has entered into a performance agreement with the member states establishing a tax performance standard for the seller. For purposes of Model 3, "seller" includes an affiliated group of sellers using the same proprietary system. (d) Model 4. Any other system approved by the department.