Dog has had diarrhea over 4 days and last day left 5 piles on rug. he challenges my dog at feedings and takes away his treats. Dog is sweet but exhausting - needs close supervision. Owners have request in for 2nd booking x 5 nights in 2 weeks, unpaid. How to handle fee, request for 2nd visit?
When I sit for a difficult dog, I let the owners know of the troublesome behavior when they come to pick him up. It can be a little uncomfortable and awkward, but if you let them know (in a kind way), they usually feel guilty enough to not book with you again. If they don't feel guilty and send you another request in the future, you can reference your prior conversation regarding the the intolerable behavior and kindly decline due to that. That's what I do.
Have you ever gotten a bad review from being honest?
If the dog is more trouble than he's worth, feel free to decline. You can explain to the owners that he just wasn't a good fit in your home and had difficulty adjusting, so you feel he would be more comfortable with another sitter (perhaps without other dogs). However, the specific issues you mentioned are easier to address if you do decide to watch him again. If the diarrhea is due to an illness, it will pass before the next stay (and if it hasn't he isn't fit to board anywhere without medical treatment in the meantime). If the diarrhea has more to do with nerves (which is fairly common) the owners should take that into consideration. It may be an indication that he was just not comfortable in your house. If he's likely to have diarrhea issues anywhere he's boarded, they should pick up some anti-diarrheal tablets like Immodium for him (for reference, my 33 lb dog can take up to 2 tablets with her meals, but usually 1 does the trick; they should consult their vet for dosing for their dog). If the diarrhea is related to stress or anxiety, it will likely get better the more he stays with you, unless it's caused by something particular to your home rather than just the adjustment. The food guarding can be managed by careful supervision at meal times and separating the dogs whenever food or treats are given.
It sounds like you should decline the request. Be honest with the owner and suggest they contact Rover Support for help in finding another sitter.