Citywide Developments Ltd (CDL) is a construction programme management company that delivers the design and build of high-value property development schemes. CDL uses third-party consultant design services, using named consultants in the contract. CDL has recently observed increases in the consultancy day rate for these consultants. Which of the following tradeable concessions could CDL offer when negotiating with the suppliers of design services, in order to achieve lower rates of pay, but without lowering the quality of service?