Stories of check-in agents making errors or not being congisant of entry requirements are legion. Often they are ignorant or make assumptions by extrapolating from one set of circumstances that they know and assuming that similar circumstances apply in all cases. (For example, it is – or was – not uncommon for passengers with an EU passport to be denied boarding, or to have to go well up the "food chain" of the airline staff to achieve boarding – if their trip apparently ended in another EU country not their own. Citizens of EU countries are permitted entry to other EU countries with no need for an onward or return ticket, so there is no problem if, for example, the trip of a British citizen passport holder ends in France.)

Some countries have slightly complicated visa regimens/visa exemptions that are not based entirely on citizenship of the traveller alone.

The wording of British immigration stamps, visas and certificates has been known to cause particular confusion – the wording is often complicated, owing partly to the complicated nature of British nationality and immigration legislation – and though the wording has been simplified in many cases, confusion can still arise, especially with airline staff whose English is not good (e.g. "leave to enter" is a particularly difficult one, since to a person with limited English, the word "leave" is likely to mean the opposite of "enter"...).

It is to be hoped that such problems are becoming less common, though it is always worth the passenger knowing what the requirements actually are.