Sign Up Process should be easier
The sign up process should be simplied. Agencies and direct advertisers do not understand if they are creating an agency or customer shell, they don't understand the difference. Agencies also don't know that they should not create their customer's accounts in the agency shell and fail to link customers.
The process could be simplified by chaning the sign up page. Bing Ads should ask right at the start if a customer wants to create an agency account or a "normal" customer account and the terms and conditions should reflect the implications if the setup is done incorrectly.