Would you trust the reply somebody like the librarian in the OP gave you?

I mean, if the answer is “no” would you just go around plugging into random Ethernet ports until you found one that works? Just because you don’t “trust” the librarian who gave you the answer? That sounds like a fast track to getting trespassed (or at least banned from using their public internet altogether) for abuse of services.

The library isn’t required to provide free Ethernet. They aren’t even required to provide free wifi. But they choose to do so because they recognize that wifi is a big reason people will come to a library to spend time. Which is sort of the whole point of the library. So providing free wifi goes hand-in-hand with the library’s ultimate mission.

But that wifi is provided on an as-is basis, because they can’t guarantee things like 100% uptime, good speeds, or any kind of troubleshooting. And any potential ethernet connection would also be as-is. And in this case, “as-is” could easily translate to “not available to the public at all.” Because again, the library isn’t required to provide any of it.