Originally Posted by
FirstInFlight
You won't win this one on the merits - meaning that you were right and he should have been allowed to board. I would try booking another trip using the same search engine and taking screen shots. If there is no warning at all - the OTA may help you (technically still your responsibility but since the industry trend is to draw attantion to that issue...). You might discover that there us a warning that was perhaps overlooked.
The next strategy would be to see if you can get a credit for some portion of the ticket value . Not what you want - but better than nothing.
Maybe the airline will issue a credit, but I don't agree the passenger should have been allowed to board. This could have resulted in more cost if the passenger arrived in China and was sent back to the USA.
It is possible the passenger may have had a visa for China - the OTA doesn't know this. Having to include a warning based on nationality for every booking made on line would be a huge undertaking.