
I work for a local dog walking/pet sitting company and I work alongside four other employees (although generally we walk dogs on our own) If a certain dog cannot go as part of a group, or there are no suitable dogs to mix with a certain dog, then the dog in question gets their walk minus traveling time. Owners are made aware that if they want their dog walked on their own (or, if their dog is only suitable to be walked on their own) they get an hour's road walk so there is no traveling time taken away from their walk. If they prefer an off-lead walk, or a walk in a particular place then they understand the time traveling there and back is taken out of their walk.
If, however, they go as a group, the hour starts from when we get to our particular place of walking. Our clients find this acceptable as they understand that we are a business and would rather take this option than pay more for a walk. For an example, if I arrive at Dog A's house at 11:03, and he is walked on his own, I return back at 12:03. If I arrive at Dog A's house at 11:03, but need to pick Dog B up on the way to the walk, then the walk starts when I get to wherever I am taking them and the dogs are brought back to the car after an hour, so Dog A could be out of the house for up to 2/3 hours depending on the size of the group.
The biggest group I take on my own is 3, and they are exceptionally well trained dogs. Generally if I have this many than I am paired with another walker and we take two each.