@Amanda1671 You should absolutely mention that in your review of the guest. That's a no-no, and it's not okay that the guest did that. That's truly obnoxious. If they did it by mistake they should simply have told you.
And as the others said, definitely block purchases by making a password required.
In my space, I provide only a smart TV and Wi-Fi. I tell guests to remember to note their log-in credentials before arriving, as they have to log in to their own Netflix and Amazon profiles to stream anything.
These days you can watch almost anything online, so I feel that providing Wi-Fi is sufficient. Good luck with your new venture! Kia