AC agents to not understand fuel surcharges. They are charged and kept by the issuing carrier, or not charged as the case may be. TG charges AC for seats on TG flights, they accept payment and htat's that. Pax do not owe anything additional, it matters not a whit to TG whether AC has billed a passenger for a fuel surcharge or not as it does not in any way effect TG's bottom line.

Now, there are reports of carriers charging passengers at checkin for missing fees -- usually when passengers think they are fuel surcharges they are mistaken, but in fact the issuing carrier simply hasn't collected proper airport taxes. That has happened to me more than once on a UA award ... UA didn't collect proper KIX departure tax and BKK departure tax.

It HAS in fact happened where a rogue, mistaken, or uninformed agent has sought a fuel surcharge. But that is not proper procedure at all.