For integrating order data from an ERP system into Sales Agreements in Salesforce, the best practice is to create specific permission sets and possibly permission set groups that grant the necessary permissions, including write access to custom objects. These permission sets should then be assigned to the integration user account. This approach ensures that the integration user has precisely the access needed without the broad permissions that would come with using a Salesforce administrator account. It also allows for more granular control and security by limiting permissions to only those necessary for the integration's functionality .