Recent personal experience:
This weekend my college-age daughter was flying British Airways from Atlanta to Budapest, via London Heathrow.
As she tried to check in, the British Air agent checked my daughter's flight record and noticed that her return date, also flying out of Budapest, wasn't for about six months. Checking her database, she said that Hungary allows U.S. citizens a stay of only 90 days, and beyond that you need a special visa. The agent asked where the visa was.
My daughter didn't have a Hungarian visa, because she's only going to be in Hungary about two weeks and then is going by train to Turkey where she is studying at an Istanbul university for the spring semester. After finishing her semester in Turkey, she's traveling in Eastern Europe and is flying back to the U.S. from Budapest.
My daughter showed the BA agent her Turkish education visa for the January-June period.
But, the BA agent said that wasn't sufficient, and she would either have to have a Hungarian visa for a six-month stay or buy a refundable or onward ticket out of Hungary departing in less than 90 days. She said that otherwise BA could be held liable and fined.
We agreed to buy a refundable ticket.
But then another nice British Airways agent offered a work-around. She volunteered to change my daughter's return ticket date to less than 90 days, at no charge, while keeping the original return date. This double-booking was done at no charge. My daughter agreed to cancel the less-than-90-days return ticket once she initially left Hungary, keeping the original return date in around six months.
It was great of British Air to do this, but it took 20 or 30 minutes and caused quite a bit of stress for everyone, including I'm sure the passengers in line behind my daughter.
As a travel writer who has dealt with this issue on a number of occasions, I should have known that this might have arisen, but I just didn't think about it, since my daughter had the Turkish education visa.
Bottom line is: Despite this agreeable ending, airlines can and frequently do enforce the letter of the immigration law.
Destination country immigration may not care, and may never ask to see your return or onward ticket, but airline agents often do, and it can cause a lot of trouble and stress just as you are trying to board your flight. Better safe than sorry.
--Lan Sluder
AmbergrisCaye.com 
