How to prevent agents or any other unwanted user from submitting customer surveys themselves in Experience Cloud?

Hi everyone,

I am working on a survey solution in Salesforce using Experience Cloud, where survey links are sent to customers via email after a case is closed.

However, I have a concern:   Since the survey link is accessible via the email record (Email Message related list), internal users (agents) may be able to open the link and submit the survey themselves, potentially giving biased ratings.

I explored a few approaches, but facing limitations:

•  CreatedBy / LastModifiedBy is not reliable, as submissions happen via site/guest user 
•  UserType cannot be trusted because survey runs in Experience Cloud context 
•  Survey link can be accessed by anyone who has it 

I want to understand:

1.  What is the best way to ensure that only the intended customer submits the survey? 
2.  How can we prevent or detect agents submitting surveys on behalf of customers? 
3.  Are there any standard Salesforce mechanisms or best practices for this scenario?

Any guidance, real-world approaches, or design patterns would be really helpful.

Thanks in advance!