Great news: there is no limit. It all depends on your negotiation skills. The more exposure and the more reach you can offer towards the merchants, the higher commissions you can ask for. Always remember that your exposure is the holy grail. Featuring merchants in special campaign articles, shop categories, social media posts, or print integrations and pushing traffic towards those channels are huge arguments for a merchant to agree on your commission requirements. Even if the deal is not always profitable for the merchant from a revenue perspective - they always profit from a branding perspective.