Direct and open honest communication is essential.
When I checked and found that the AC was not functional. A quick troubleshoot found out why: the control unit of the AC was missing. When I contacted Arnaud, it seemed very disingenuous by asking for a picture of the actual remote (how can that tell anything?). When I sent an additional picture of the missing control unit and to inform that I knew how to troubleshoot. No attempt to apologize or offer a refund after I told him that the unit is uninhabitable without a functioning ventilation.
More precisely, after I told him I could not stay, he simply essentially replied: “I understand”. That told me all I needed to know - he already knew of the issue.