Third party resellers can be effectively prevented by limiting the warranty and return policy to the original owner, which is a pretty common practice in many industries.

That's more difficult to accomplish with consumer products. Consumer protection laws (legislative and, to an extent, common law) limit contractual flexibility in that regard. If you sell something to the general public, it can be difficult to discriminate "business" purchasers, which is why retail arbitrage has always been a thing--a legitimate and legal thing.

The usual way to discriminate is by selling to businesses through a separate distribution channel with separate contractual controls. But to convince businesses to purchase through that channel you either need to sell into the channel at a lower price or otherwise provide some value-add. But that's exactly what Tesla refuses to do--sell through multiple channels.