Passengers are being left out of pocket even when their internet booking mistakes are down to glitches in airlines' own systems, an air customer group has claimed.
Complaints from passengers about problems making reservations have more than doubled in the last few years, said the Air Transport Users Council (AUC).
The council has now written to the chief executives of the airlines involved, asking them to put policies in place which are "more customer- friendly".
In one case highlighted by the AUC today, a father buying four tickets for a bmibaby flight was asked to pay an extra £340 after his booking showed that all the tickets were in his name and needed to be changed.
He cancelled his tickets but was refused a refund and therefore spent £452 on flights which he never took, the AUC said. In another case, a woman passenger, told that her booking could not be processed "due to unforeseen circumstances", decided to book through another website.
Checking her email later, she found her first booking had, after all, gone through and she now had two tickets for the same flight. The AUC said the first airline had initially refused to refund her but did so after the AUC intervened.
Another case involved a male passenger who is still trying to get back a £35 "administration fee" charged by an airline after the man had been charged twice when his debit card was rejected the first time.
AUC chairman Tina Tietjen said today: "In the last few years the number of complaints to the AUC from passengers who have had problems making reservations for airline tickets has more than doubled. The majority of these complaints were about reservations made through the internet.
"Complaints to the AUC show that a number of airlines regularly leave passengers out of pocket following innocent mistakes or, sometimes, it appears, even if there are glitches in their own booking systems.
"Reservations systems do not always work smoothly and we believe that the risks of booking over the internet should not be always be loaded on to passengers."
She went on: "We have therefore written to the chief executives of those airlines about which we have most unresolved complaints in this area and asked them to put into place polices that are more customer-friendly.
"We have suggested a policy where their airlines voluntarily commit to providing a 24-hour cooling-off period in which passengers can cancel their reservations free of charge within 24 hours of making a booking."