Well, if the other site was able to provide an actionable error message, it must be possible. It might not be in the website’s direct control, but they are in control of which payment processor to use.
that assumes that there is a clear ranking of payment processors and that the processor that is crap at one moment in time is crap at all moments in time and the processor that is good at one moment in time is good at all moments in time and that the momentary superiority of one payment processor is an absolute superiority that makes them the obvious choice and anyone not making that choice is bad.
Which is, admittedly, a very HN assumption to make on basically any subject that comes up.
No, my assumption was that the original poster hadn't ever worked e-commerce or they wouldn't have complained in a way that they thought it was inevitably due to factors within the sites' control that one worked nice and one worked crappy on this particular factor.
To an end customer, it doesn't matter if a problem is under the merchant's direct control or if it's happening upstream. He is the merchant's customer, the UX he sees is how the merchant is choosing to represent itself to their customers, and therefore the merchant, and only the merchant is accountable if that experience is crappy.
Whether OP actually worked in e-commerce is kind of irrelevant. I've never worked in e-commerce either, and if CompanyX fails to process my payment and I can't buy something from them, I'm going to rightfully blame CompanyX for that, not one of their service vendors.
I think maybe you are overreacting. No one is saying they’re bad or stupid. It is understandably difficult to get right when they probably have very limited insight into why some people might abandon a payment.
But in the end, the effect is that they lost a sale to a competitor who got it right this time.
Which is, admittedly, a very HN assumption to make on basically any subject that comes up.