I think you're taking it too personally.

As previously noted, popping hotswap sockets is common. There's a reason they've posted a video on how to insert switches, why it's noted in the assembly card that comes with the board and is called out in the build guide. Or look at any other vendor's build guides and they all warn about popping hotswap sockets. It's not because of the quality of the products but because it is a very common mistake. So if I were a vendor and a customer came to me that a key wasn't working in a hotswap board, it's not crazy to think that the first place to start is asking if they inserted their switches properly.

To me this seems like nothing more than them starting with one of the most common problems with non-functioning keys on a hotswap board (improper switch installation) and then going from there. They're not blaming you out of the gate but are just going through the process of elimination with one of the most common causes for this issue. I own 4 NK87s and an NK65 and from multiple production versions and never had an issue with a hotswap socket not being properly sodered.

Sorry they're not the vendor for you because I really do like them. Best wishes on all your future builds and hopefully you don't have more customer support issues like this in the future!