You're just letting your renters access your personal Roku account?
If you log into your account at https://my.roku.com you can create or reset a PIN value. You can then choose when the PIN is to be required, such as before it will allow any subscription or purchase to be made on your account. Without knowing the PIN that would prevent ANY purchases by your guests.
Have you looked into Roku Guest Mode? https://support.roku.com/article/360015612834
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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