I mean, the worst. Only matched by health insurance companies.
The huge problem with Amazon support is everyone I've ever interacted with (besides that one time I got forwarded to a supervisor) either have a fundamental lack an understanding of the English language or lack reading comprehension (or listening if phone support). They also won't or can't spend any significant time on any one customer inquiry, they need to move onto the next.
On the buyers side they understand how to refund an order which they do readily, ship items, say you can keep items that are errors, maybe some account stuff, and that's basically it. If you need them to do anything else that requires them to understand your inquiry it's an uphill battle.
Basically, you get terrible support if your inquiry can't be solved by quickly pressing the "refund" button or the "ship item" button. I guess most buyers usually only need those two buttons though.
I actually think that's part of why they have such a big problem with counterfeits (and other issues). If someone complains about a counterfeit some low paid employee who doesn't really understand the problem just presses "refund order," the customer stops complaining, and the systemic issues remain.
I have a nightmare Amazon seller support story, but I won't go into it for fear of spiking my blood pressure to dangerous levels. It was only resolved by me finally getting forwarded to a supervisor, who, finally, understood English.