What is the ruling on working for a company that exports carpets to Europe, knowing that 20% of the orders are for casinos?

There is no harm in providing the requested carpets, and you are not obliged to inquire about the buyer's intention for their use, as the basic principle in selling is permissibility. However, if you know before the sale that the buyer will use the carpets for a wine bar, then it is forbidden for you to sell to him, due to it being cooperation in sin and aggression.