I mean, I'd argue that afterward that it's an unreasonable charge. But the prudent thing to do is always ask.
Agreed, but if he asked the discussion is a non-starter. Hypothetically speaking, either he was told there was no charge and that's grounds for contesting any charge (even $1), or he was informed and used the service in which case he shouldn't have. If he was told the charge was a reasonable amount the bill should be adjusted to reflect what was quoted.