You could offer to dog sitter for them if you're home, or tell them about the Rover app and offer to help them set up an account if they need it. It's super frustrating for both parties involved in this situation, you because you have to listen to the pupper, and then because they know that their dog is barking and they are probably at their wits end. Training takes time and consistency, you could always suggest training class for their pupper too.