Communication is the key to minimizing risk and optimizing outcome. Some agencies will use a chain of communication whereby you’ll communicate only with the account manager or director. While others utilize a system in which you communicate directly with the person executing tasks. The communication style will generally be dependent on the size of the agency. The best way to keep channels of communication open no matter the structure is to be transparent – talk about your long-term objectives and give regular feedback.
The whole process of on-boarding a new agency shouldn’t be too different to looking for your next employee to hire. They should be considered as part of your team and not a third-party extension. Work out who it is in your team that will be dealing with the agency most and bring them along to pitches. By doing this you’ll guarantee that not only you, but also those working closely with the agency, are comfortable with the decision.
A final thought – I see choosing an agency as a very similar process to getting married. Don’t rush into it, take your time in researching your options and make sure you’re 100% comfortable with your choice before finalizing the decision.