This study comprehensively analyses the contractual T&Cs governing the relationship between online platforms and their professional users, reviews the legal framework regarding such T&Cs in 33 countries and suggests fairness benchmarks for this contractual relationship. The aim of the study’s first part (Task 1) is to gain an understanding of whether and, if so, how online platforms' T&Cs negatively affect existing and potential professional users. To this end, the study analyses the T&Cs and community guidelines used by a wide set of online platforms. It covers 102 platforms, with a broad and appropriately balanced mix of platforms, including both large and small players, and a balanced geographical coverage. Given that a number of the large platforms (for example Amazon, Facebook, Ebay, Expedia, Salesforce, Uber, Rakuten, Zalando, Groupon, Spotify, ASOS) have been included in the review, a significant part of the overall B2B platform business within the EU is considered within this study.