As you can see from the wikipost, most of the backwards stupid anti-free market states just have a rule that car mfr can't control or operate a car dealership. That's all. Not too complicated or arcane.
a manufacturer or distributor may not directly or indirectly; (1) own an interest in a franchised or nonfranchised dealer or dealership;(2) operate or control a franchised or nonfranchised dealer or dealership; or (3) act in the capacity of a franchised or nonfranchised dealer. (Tex. Occ. Code Ann. § 2301.476)
"A motor vehicle shall not be advertised for sale in any manner that creates the impression that it is being offered for sale by the manufacturer or distributor of the vehicle. An advertisement shall not contain terms such as “factory sale,” “fleet prices,” “wholesale prices,” “factory approved,” “factory sponsored,” “manufacturer sale,” use a manufacturer's name or abbreviation in any manner calculated or likely to create an impression that the vehicle is being offered for sale by the manufacturer or distributor, or use any other similar terms which indicate sales other than retail sales from the dealer" (43 Tex. Admin. Code § 215.261).
A manufacturer shall not do any of the following: . . . (h) Directly or indirectly own, operate, or control a new motor vehicle dealer, including, but not limited to, a new motor vehicle dealer engaged primarily in performing warranty repair services on motor vehicles under the manufacturer's warranty, or a used motor vehicle dealer. Mich. Comp. Laws Ann. § 445.1574