Hi Sarah,
Thank you for reaching support. The customer(customer-account) can make the API calls using the OAuth credentials from a manager account and accessing a related administrator-account. With regards to your concern, you should generate the credentials for administrator-account and share it with customer-account if you don’t want your account to be linked. The customer-account can use either developer token or your developer token to make the API calls. Please note, it is not recommended to share developer token unless they are making API calls against your account. Also, the operations you are performing in the API call will be counted towards to the Developer token used in the API call.
Regards,
Nikisha Patel, Google Ads API Team