France is not Spain, but both are civil-law jurisdictions, so I expect this answer to be marginally more applicable to the original question than answers based on common-law countries.
Listed prices are binding on the seller, even if mistaken
Price tag errors (whether physical or electronic) usually involve low amounts of money, so there is not much jurisprudence on that point. Let us start by discussing Cour de cassation, Chambre civile 1, 04 juillet 1995, 93-16198, where the highest French court endorsed a 1993 court of appeal ruling, because it illustrates some relevant principles.
A jewelry store put up a ring for sale for 100 000 francs (equivalent to roughly €20 000 in 2021), which someone bought. The store later realized that there was a mistake in the price tag (the intended listing price was more than four times higher) and sued to revert the sale.
The court of appeals judged that
- as a general rule, mistakes in price tags are a risk the seller takes;
- the buyer could reasonably think the asked price matched the true value of the ring, and therefore it was not "unrealistically low"
The latter point refers to a statute (Code Civil 1169) that says a contract of something-for-money is void if the price is "unrealistically low". The ruling essentially says that the test for "unrealistically low" is whether the buyer should reasonably be aware that the price is due to a mistake from the seller.
I doubt a store can rely on the "unrealistically low" provision in the case of shipping fees. A random consumer has no way to accurately know the price of overseas shipping. Even if they did think the shipping fees were much lower than expected, it might be because the store chooses to charge something else that their exact costs, for whatever reason (e.g. uniform shipping fees is easier to maintain on their website that one cost for each country; some stores are "free shipping" meaning they recoup their shipping costs with higher item prices).
No surprise fees
The seller might argue that their shipping costs were unknown, and that the shipping fee they charged was a provisional estimate, or conditional on a later determination of the true cost.
Code de la consommation, L112-3 says that when the total price of the item or service sold "cannot be reasonably known in advance [of the sale]", the seller must provide advance notice to the buyer, as well as the method by which the unknown components of the price will be later determined. No such notice appears to have been made.
Online sale: when is the contract formed?
The seller might argue that clicking "buy" on an online shopping cart does not form a contract, but that they reserve acceptance at a later date. The other answers seem to indicate that is a valid practice in some common-law countries, but I believe that is not the case in France. I could not find court cases on exactly that point, and therefore cannot be sure that the rest of my answer is correct.
I believe the seller is bound by the terms offered on the website, based on Code Civil, 1127-1 and 1127-2.
Quiconque propose à titre professionnel, par voie électronique, la fourniture de biens ou la prestation de services, met à disposition les stipulations contractuelles applicables d'une manière qui permette leur conservation et leur reproduction.
L'auteur d'une offre reste engagé par elle tant qu'elle est accessible par voie électronique de son fait.
Le contrat n'est valablement conclu que si le destinataire de l'offre a eu la possibilité de vérifier le détail de sa commande et son prix total et de corriger d'éventuelles erreurs avant de confirmer celle-ci pour exprimer son acceptation définitive.
Whichever business proposes by electronic means the sale of goods or services must allow the contractual conditions be be recorded and reproduced.
The author of an offer is bound by it as long as it is accessible due to his or her actions.
The contract is formed only if the recipient of the offer could check the details of his or her order, its total price, and could correct possible mistakes, before confirming the order to formulate his or her definite acceptance.
"Due to his or her actions" means I cannot screenshot an Amazon page (or duplicate it on my web server) and request the conditions of that screenshot two years later. However, it does not include provisions for mistakes in the listed price or sales conditions, and I would expect the general rule (price tag mistakes are on the seller) to apply on the internet.
The last paragraph cited is a consumer rights provision - essentially, "no contract is formed unless the consumer did X". However, it implies that once the consumer did X, the contract is formed.
For the above reasons, I believe clauses that allow an online store to unilaterally cancel an order once placed are unenforceable (unless force majeure or other narrow exceptions apply). That being said, the incentive to sue in such cases is low (and I could find no jurisprudence).
In France (and I believe in all civil-law systems), civil liability is established by three factors: a damage, a wrongful action, and a causation link between the two. In the jewelry case, the store could easily prove the damage (difference between the price at which the sale was made and the price at which the item was estimated), and the causation link between the consumer’s action and the damage; however, there was no wrongful action.
In the case where the exchange of goods against money has been blocked by the store, the consumer’s problem is to prove damage. If they have not been charged, or if they have been charged but refunded, the direct monetary impact is zero. The consumer would have to prove other theories of damage: for instance, that they relied on the ordered item to do something, and could not find a replacement in time. However, in all such scenarios, the causation link will be hard to prove.