There’s definitely something going on with this dog that isnt right, for whatever reason behavioural or medical… As you’ve done I’d suggest to the HO they should get him/her checked out, and I would also withdraw from the sit because it wouldn’t fit with what i’d want to do.
Actually the owner decided I wasn’t the right fit when I asked if she’d taken her dog to the vet, but I was going to withdraw anyway and did
My sister in law has two small sister dogs.
One never stops. You could literally walk her for hours, and she’d still play ball all day. The other, 10 minutes and she’d stop. Luckily shes small enough to be carried but she actually started to hide when it was walk time because she didnt want to go out., though she’d happily go in the garden.
We just accepted their different personalities and energy levels, like people. Now she has a doggy push chair & while one is happy to walk, the orher is happy in the chair.
As it’s gotten warmer and more humid out here, I’ve noticed my little dog is not a fan of being outside or going for walks (even short walks). He will do his business and then just stop. I check the concrete with the 7 second back of my palm to see if it’s too hot and it’s normally fine, but I think the humidity really gets to him. I mean, it gets to me sometimes! Not to mention the bad air quality we’ve had in the Midwest because of the Canadian fires. In which case when the quality is really bad we keep our walks super short (potty and then go inside).