Italian to English Law/Patents Law (general) criminal case - interrogation

This term is being used to describe a contract with a consultancy where the consultant was supposed to be helping a supplier, through his relations with the principal, to secure a supply contract. I thought of 'advocacy', consultancy does not capture the sense, and I also thought of 'agency' and 'representation' but again, these do not seem to capture the sense of persuasion/influence. I was just wondering whether anyone had any better ideas or any views on advocacy? TIA.