My landlord has issued me by bailiff leave for sale with indication of a net selling price. The real estate agency in charge of the sale claims me €30,000 agency commission. Do I have to pay them?

No. The Court of Cassation in a judgment of July 13, 2013 (No. 12-19442) specified that "the tenant with a pre-emptive right accepting the offer to sell the property he lives in and who does not have to to be presented by the real estate agent, commissioned by the owner to search for a buyer, can not be imposed the payment of a commission increasing the price of the property."

You are therefore not liable for €30,000.