Do my clients have to sign up to an account to leave a review?

If you're a basic subscriber

Yes, your clients will need to sign up for an account to leave a review. 

If you're a premium subscriber

No, you can shortcut the process by distributing your unique survey link. Clients can also submit private feedback if they feel more comfortable doing so, which is a great way to keep on top of your customer satisfaction and quality control. 

This is vital for word-of-mouth growth.