If you decide to monetize your app through in-app purchases/subscriptions, commission to each app store will vary. If your app is listed under your own developer account, MAZ will no take any commission from your sales, it will only be between you and the respective app store.
Apple & Google
Both Apple and Google will take a 30% commission and you will collect 70% of sales from in-app purchases.
Additional reference for Google.
Amazon charges a 15% commission on sales from in-app purchases.
Additional information can be found here as well as in the Amazon Developer Services Agreement.
Roku will charge a 20% commission on sales from in-app purchases.
More information directly from Roku here.