First off.... you cannot legally/safely download an app for iOS (either iPhone or iPad) without going thru the Apple Store. Unfortunatly this is the way it is. As such, the developer has NO IDEA who has downloaded their app, has no access to any "database of users", nor can they blacklist a user .... Only Apple can do that.
None of this applies to macOS applications however. Other than they must be "notoraized".... A developer is free to sell in the App Store, AND sell on their own, in which case they know who THEY sold to, but again not who bought it via the store.
So, if they are offering you any "deal" (other than a promo code).... WALK AWAY
None of this applies to macOS applications however. Other than they must be "notoraized".... A developer is free to sell in the App Store, AND sell on their own, in which case they know who THEY sold to, but again not who bought it via the store.
So, if they are offering you any "deal" (other than a promo code).... WALK AWAY