Is it unreasonable to expect pet owners to provide clean conditions and 1/2 way trained dogs?

No, it's definitely not unreasonable, but you have to be the one to enforce a level of cleanliness and training that is appropriate for your services. I totally understand wanting to be there for someone last minute--I've done it, resulting in both good and bad experiences. Sometimes it's a good way to make a loyal client, but sometimes it results in way more effort than it was worth. No matter how badly I feel for someone, I have to step in and say when I am not going to be a good match for their needs and what I can reasonably do for them. In your case, taking on the client but insisting on not staying the night is a good compromise given your standards. It sounds like you're making your money on this one. If it were me I wouldn't return the fee.

As a dog sitter you should always meet with the customers and talk about your responsibilities and if you'd be staying the night or not. Only agree to caring for a dog if both the owner and the dog is a good fit. Politely decline any requests that are not a good fit.

In the event of a misunderstanding you should contact the rover support center for help to ensure the issue is resolved.

If you have concerns about cleanliness you may politely communicate them to the dog's owner and let them know what will you be doing to make yourself more comfortable; if you don't feel up to the task of cleaning up for your comfort that might not be a good fit for you. Never demand the customer to clean the house themselves.