(28)Card-based payment transactions are generally carried out on the basis of two main business models, so-called ‘three party payment card schemes’ (cardholder — acquiring and issuing scheme — merchant) and ‘four party payment card schemes’ (cardholder — issuing bank — acquiring bank — merchant). Many four party payment card schemes use an explicit interchange fee, which is mostly multilateral. To acknowledge the existence of implicit interchange fees and contribute to the creation of a level playing field, three party payment card schemes using payment service providers as issuers or acquirers should be considered as four party payment card schemes and should follow the same rules, whilst transparency and other measures related to business rules should apply to all providers. However, taking into account the specificities which exist for such three party schemes, it is appropriate to allow for a transitional period during which Member States may decide not to apply the rules concerning the interchange fee cap if such schemes have a very limited market share in the Member State concerned.