As you already know, you can create users for each client so they can log in and view their analytics at any time. If you don't, here is an article on how to do so. https://support.tourbuilder.com/hc/en-us/articles/360000639054-Lesson-27-Creating-User-Logins-for-Your-Clients
By creating a user for your client, they can log in and see the tours you have created for them, including the custom tours that have not been paid for yet. This is how you can have them preview the tour before paying.