If you are providing someone a service, and you rely on a third party to provide that service, and that third party screws you over, then by extension, you are

If you are providing someone a service, and you rely on a third party to provide that service, and that third party screws you over, then by extension, you are screwing over your customers. That is your fault, and your customers have every right to blame you. You are responsible for the due diligence on which providers you use. Blaming a 3rd party might absolve you of some of the blame, but your still not providing the service you agreed to provide. And before you try to suggest anything else, the condition here was "having customers you can't let down." You have customers you can't let down. That's the context.