Can I stop the price changing between the search results and the payment page on my website?

No, you cannot stop it happening altogether, but you can make it rare and make sure the customer is told about it properly when it does happen. Live travel prices are never fixed until the supplier confirms them, so any booking website in the world can show one price in the search results and a slightly different one at the end.

The reason is simple. When a customer searches, the portal shows results that were collected from the airlines, hotel suppliers and consolidators a short while earlier, because going back to every supplier for every search would make the site far too slow. Seats and rooms sell all day long and suppliers change their rates constantly. When your customer picks one option, the system goes back to that supplier to confirm it, and the supplier may come back with a different price, a sold out room, or extra taxes and baggage charges that were not in the first screen.

What a well built B2C portal does is check the price again before the payment page, show the customer clearly that the price has moved and ask them to accept it before they pay. How often this happens depends on the supplier and the type of connection, so low cost airlines and dynamically priced hotels tend to move more than negotiated contracted rates. Some suppliers also let you hold a price for a short time, and where that is offered the portal can use it.

If customers are complaining about this, watch which suppliers the changes are coming from and raise it with your technology provider, as the length of time results are kept before being refreshed can usually be adjusted.