Will my customer ever be asked to pay more than the price they saw when they searched for a flight?

Yes, it can happen, although it is not an everyday event. Airline fares are live, so the price your customer sees in a search result is the price the airline was offering at that exact moment. Seats are sold in small buckets, and when the cheapest bucket is taken by someone else, anywhere in the world, the next price becomes the one on offer. If your customer searches in the morning and comes back in the evening to pay, they may find the fare has moved.

To protect you from this, the booking flow normally checks the fare again just before payment is taken. If the price has changed, your customer is shown the new amount and asked to accept it before anything is charged, so you are not left covering the gap out of your own pocket. If the fare is still the same, the booking goes through as expected and nobody notices a thing.

How much warning you get, and whether a fare can still move after payment, depends on the airline and the supplier behind the search. Low cost carriers tend to change prices far more often than full service airlines, and some suppliers will hold a quoted fare for a short window while others do not hold it at all. We cannot promise a fixed price across every airline on your site, because that decision sits with the airline and the supplier rather than with us.

If this matters a lot to your business, ask us which of your flight suppliers allow a fare to be held, and tell your staff to finish the payment in the same sitting as the search so there is less time for the price to move.