Weak contestability and unfair practices in the digital sector are more frequent and pronounced for certain digital services than for others. This is the case in particular for widespread and commonly used digital services that mostly directly intermediate between business users and end users and where features such as extreme scale economies, very strong network effects, an ability to connect many business users with many end users through the multisidedness of these services, lock-in effects, a lack of multi-homing or vertical integration are the most prevalent. Often, there is only one or very few large undertakings providing those digital services. Those undertakings have emerged most frequently as gatekeepers for business users and end users, with far-reaching impacts. In particular, they have gained the ability to easily set commercial conditions and terms in a unilateral and detrimental manner for their business users and end users. Accordingly, it is necessary to focus only on those digital services that are most broadly used by business users and end users and where concerns about weak contestability and unfair practices by gatekeepers are more apparent and pressing from an internal market perspective.