I have the same sketchy feeling about Sofortüberweisung/Klarna. If they want to make transactions on my behalf, why should I give them full access to my account

I have the same sketchy feeling about Sofortüberweisung/Klarna. If they want to make transactions on my behalf, why should I give them full access to my account? Most banks have a paragraph in their contracts/ToS forbidding sharing the account with third parties, but they are rarely enforcing it. Still, they could close the account due to contract/ToS violation.