Site migration on client level
There should be a way for clients to be able to migrate from one provider to another between servers without problems and server administrator involvement.
Anonymous shared this idea
Plesk backup contains not only clients data but configuration data, limits and so on. Migration from one Plesk to another on customer level is prohibited due security reasons. Unverified 3rd party backup can be used to compromise your server. I'm going to edit your request to make it more suitable.