It will also shape the type of agency you need. This is usually determined by what you do, where and how you trade. If you're a US company setting up in Europe, look for an agency with established US-EMEA performance already. The closer the fit, the more likelihood of success. Ask the agency for their Credentials document.
Every agency has one - it's a straightforward summary of services, strengths and existing clients.
Select the size of agency with care You want to be a valued client so choose an agency that will value your business. Generally speaking smaller companies should choose smaller agencies. You want to be the first thought on a Monday, not the last thought on a Friday. Make sure the agency has the capacity to handle your account. Make sure you meet the doers As with all business, success depends on good personal relationships.