As a CSP partner, we currently use the MSOL cmdlets for our automation process. We are currently switching our implementation to Microsoft Graph API.
MSOL offers, through Get-MsolSubscription, a way to know if a subscription has been bought by us or by another service provider. To know that, we inspect the OwnerObjectId attribute and if the value is set with our Id, we know it has been bought to us. Otherwise this attribute is empty.
It seems that Microsoft Graph API does not support this feature. SubscribedSku does not seem to expose the feature we are looking for.
Any ideas?