At least in our experience, the first line of support is from the chassis vendors. You don't go to a store and buy MI300x. You buy them from someone like SMCI/Dell, who provides the support. Of course, behind the scenes, they might be talking to AMD. Even those chassis companies often have other providers of their gear (like Exxact) as another line of defense as well.

In the case of Groq, it would have been death by 1000 cuts to have to support end users directly, especially if they are selling small quantities. It is much easier to just build data centers full of gear, maintain it yourself and then just rent the time on the hardware.