Being barred from a flight despite a valid booking, a ticket in hand, and having arrived at the airport in good time is a global phenomenon, thanks to airlines' policy of overbooking in an attempt to get maximum bums on seats. Naturally, "bumped off" passengers are not happy. Fortunately, the Consumer Protection Act does compel airlines to compensate them.Mango airlines has been barring passengers despite their seats being available, causing all kinds of drama at boarding gates and check-in counters.In the case of tickets purchased with a credit card, Mango insists that the credit card used be produced, or at least a photo of it.When the ticket was paid for by a third party, and neither they nor the traveller was aware of this policy and thus didn't make an image of the card available in time, the consequences have been devastating.It happened to me two weeks ago. I was due to speak at a conference in Midrand, my ticket having been paid for by the conference organiser by credit card, a copy of which was not sent to me.I had checked in online, but was told to stand aside when I tried to board. I got hold of the organiser, who sent me a photo of the card used, but the Mango crew member insisted it was the wrong card.It was only thanks to the intervention of Mango's communication manager, Hein Kaiser, that I was able to board the flight at the last minute.Last week, Alan Cooper and two fellow journalists, who had flown from Durban to Joburg for a press conference, were barred from their Mango flight home that evening due to lack of card proof."The crew manning the boarding gate did say we could buy new tickets - at R2500 each - right there," Cooper says.Their host couldn't get the card proof to the boarding gate in time and they were unable to get on to a later flight, so all three were forced to stay overnight at an airport hotel and get a 6am flight home at R2200 each, causing enormous personal disruption.And I've since heard several other anecdotal stories of both leisure and business travellers being refused entry to Mango flights because of the airline's credit card policy.Can Mango do this, legally? Well, yes, if it adequately discloses its credit-card policy upfront.I had another look at the confirmation e-mail I had been sent by Mango when I had checked in online. Towards the bottom, the disclosure appears: "At check-in, the guest must present both the credit card used to make the booking, and some form of identification."Given that Mango is currently the only airline implementing this policy, the disclosure should be more impossible to miss, and included on online boarding passes in huge letters, in my view.I asked Kaiser when Mango began to enforce its credit card policy strictly, and why, given that other airlines aren't doing the same."The procedure is in place to protect cardholders due to the enormous amount of credit-card fraud around," he said."We do communicate this in our terms and conditions as well as on all booking- confirmation e-mails and in media releases over the years."But the airline is clearly rethinking its stance. "We are presently investigating different options to this process in order to minimise inconvenience to our guests while simultaneously protecting cardholders," Kaiser said.Good move. Routinely alienating and grossly inconveniencing legitimate would-be passengers is not in anyone's interests.Credit-card fraud is clearly a huge risk to all online businesses. So how do other airlines protect themselves without demanding sight of the cards used to pay for tickets?Shaun Pozyn, kulula.com's head of marketing, says its automated systems "check and recheck" the validity of credit cards to identify potential fraud attempts speedily and prevent the transaction from being successful."If a suspicious card transaction is detected, but is able to pass all the automatic 'fail' conditions, the transaction is flagged for immediate human investigation," he said."We are constantly investigating ways to further reduce card fraud and minimise any impact on our legitimate customers."CONTACT WENDY:E-mail: consumer@knowler.co.zaTwitter: @wendyknowler..