Why are surveys displaying a different staff account than the one that handled the incident?
If you want your surveys and mailings to display the name of the staff account that handled the incident, you can use the 'Assigned Account' (incidents.assgn_acct_id) merge field from the Incidents table.
Surveys or any other Outreach emails are associated with contacts and not incidents. Therefore, when using the 'First Name' (accounts.first_name) merge field from the Accounts table the system is going to try to find the value of an account that is associated with the contact. The value that is being picked up is from the SalesPerson field (contacts.sales_acct_id) which is the result of a join between the Accounts and Contacts tables.
For additional information, refer to the 'Viewing the data dictionary' section in online documentation for the version your site is currently running. To access Oracle Service Cloud manuals and documentation online, refer to the Documentation for Oracle Service Cloud Products.