[Wrong behavior] Already recorded transaction

I have two way to buy same product (non-consumable). When I fully test first one and switch to second I get "Already recorded transaction" when I try to test purchase same item.
Question: If the item is already purchased isn't it correct to fire purchase success event rather than throwing a useless exception?

 

Sorry I don't quite follow. You should get an exception when trying to purchase the same non-consumable product again. You should design your app so you don't allow the user to purchase a non-consumable a second time.

 

Ok.
Question II: Where I can find info about handling IAP on android, for example when app is uninstalled and installed again, how to recover user's purchases ?

 

Non-consumable purchases will be automatically restored, you can expect to get a ProcessPurchase callback. For other purchases, you can save the purchase history in PlayerPrefs.

 

https://docs.unity3d.com/Manual/UnityIAPBrowsingMetadata.html
Unity IAP retrieves localized product metadata during the initialization process, which you can access via the IStoreController’s products field.
Are these products from store or user bought(local)?

 

Both. You can check item.hasReceipt during initialization. There is an example IAP project here: https://forum.unity.com/threads/sample-iap-project.529555/

Code (CSharp):

1. m_StoreController = controller;
2.         m_StoreExtensionProvider = extensions;
3.         foreach (var item in controller.products.all)
4.         { ....