As I said, I don't live in the US but I've heard that there, bills are negociated by insurances afterwards. It's a shame that the patient has an unexpected bill

As I said, I don't live in the US but I've heard that there, bills are negociated by insurances afterwards. It's a shame that the patient has an unexpected bill to pay (and I think a good part of trouble/resentment stems from there). Here it seems like they were not warned about it (whereas we are where I live) and that's the only reasonable explanation I could think of. But maybe someone from there can shed light on why the exam the patient agreed upon came back as an unexpected bill, instead of incomprehensible downvotes ?