You have bought your trip (tour, holidays, or flight), from a service provider (travel agency or on-line).
You must know that even once your reservation is signed and your first instalment is paid, the seller can legally rise the price of the trip if he is himself subject to a rise in cost due to the price of oil or to the variation of the exchange rates.
Beware, only trips reserved a month in advance are subject to price changes. If you buy a trip and leave within the thirty days, you are not concerned by this measure.
Don't forget to check that all these precisions are indicated in the pricing terms and conditions of your tour operator.
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