What does "best efforts" mean in the world of investment banking? Investment banks make their best efforts to provide accurate quotes to clients for available for sale securities. Investment banks provide assurance and insurance for performing proper due diligence on Mergers & Acquisition deals. Investment banks will provide the best available interest rates for margin lending and stock loans or will act as a broker to find the counterparty that does provide the lowest rates/fees. That a capital markets deal will be brought to market with the investment bank's best effort" but the investment bank will not post any direct capital support to provide a minimum amount and/or price