The national court had to itself assess whether a contract term is unfair, referring to Banco Espanol v Camino and Banif Plus v Csipai.
That criterion corresponds to the idea on which the system of protection implemented by the directive is based, namely that the consumer is in a weak position vis-à-vis the seller or supplier, as regards both his bargaining power and his level of knowledge.
This leads to the consumer agreeing to terms drawn up in advance by the seller or supplier without being able to influence the content of those terms (see, inter alia, Case C‑618/10 Banco Español de Crédito [2012] ECR, paragraph 39, and Case C‑472/11 Banif Plus Bank [2013] ECR, paragraph 19).
The consequences of the inequality existing between the parties are aggravated by the fact that, from an economic perspective, such a contract relates to an essential need of the consumer, namely to obtain lodging, and involves sums which most frequently, for the tenant, represent one of the most significant items in his budget, while, from a legal perspective, this is a contract which, as a general rule, is covered by complex national rules about which individuals are often poorly informed.
In the light of the foregoing, the answer to the first question is therefore that the directive must be interpreted as meaning that, subject to contractual terms which reflect mandatory statutory or regulatory provisions set out by national law, which is a matter for the national court to ascertain, it applies to a residential tenancy agreement concluded between a landlord acting for purposes relating to his trade, business or profession and a tenant acting for purposes which do not relate to his trade, business or profession.
As regards the issue of whether the national court, in the case where it has established that a penalty clause is unfair, can merely mitigate the amount of the penalty provided for by that clause, as it is authorised to do in the present case by Article 94(1) of the BW, it must be observed that it is expressly provided in the second part of Article 6(1) of the directive that the contract concluded between the seller or supplier and the consumer is to continue to bind the parties 'upon those terms' if it is capable of continuing in existence 'without the unfair terms'.
In this connection, it has pointed out that, given the nature and significance of the public interest which constitutes the basis of the protection guaranteed to consumers, the directive requires Member States, as is apparent from Article 7(1) thereof, to provide for adequate and effective means 'to prevent the continued use of unfair terms in contracts concluded with consumers by sellers or suppliers'.
If it were open to the national court to revise the content of unfair terms included in such contracts, such a power would be liable to compromise attainment of the long-term objective of Article 7 of the directive, since it would weaken the dissuasive effect on sellers or suppliers of the straightforward non‑application of those unfair terms with regard to the consumer (Banco Español de Crédito, paragraphs 66 to 69).