“App licenses are provided to you by Apple or a third party developer (“App Provider”). Apple acts as an agent for App Providers in operating the App Store and is not a party to the sales contract or user agreement between you and the App Provider.Apple's development agreement with respect to the App Store has traditionally specified that Apple is permitted to take responsibility for all that – hear from customers, offer refunds, and so on. Relieving small developers of that burden, allowing them to focus on actually providing their apps, was presumably the whole point of that.
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Subject to local law, the App Provider of any Third Party App is solely responsible for its content and warranties, as well as any claims that you may have related to the Third Party App
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Apple is responsible for providing maintenance and support for Apple Apps only, or as required under applicable law. App Providers are responsible for providing maintenance and support for Third Party Apps.
https://www.apple.com/legal/internet-services/itunes/