Dog-sitting a non-housebroken dog?

[Dogsitter]

Hi,

A question for dog-owning forum-readers: in your opinion, is it reasonable to ask someone to dog-sit if the dog isn't housebroken?

We've been looking after our neighbor's six-year old son once a week, mostly to give her (a single mum) an evening off. He's a good kid, and we enjoy spending time with him.

A year ago, she got a shih-tzu puppy. He spends most days alone at home, and not surprisingly, a year and a half later, he's still not housebroken. While the mum hasn't been outright asking us to take the dog when we pick up her son, it's somewhat implied. The few times that we've had the dog over, he's frequently peed and occasionally pooped indoors. My partner thinks that looking after the dog (at our house) is part-and-parcel of looking after the six-year old. I think that, while it's sad and unfortunate that the dog is basically neglected during the day, it's within our rights to say no to dog-sitting in this case.

What are your thoughts? Would you ask a friend to look after your dog if it wasn't house-trained? Alternatively, would you agree or decline to do so if you were asked?