Around here, the dog-adoption places welcome volunteers who exercise and play with the dogs. Also, the main dog-adoption place and some of the dog-rescue organizations rely on "foster-homes" for dogs.

Taking care of someone else's dog while they are on vacation, or regularly walking a dog for someone else who can't manage it, would at least give you a better idea of how close your life is to fitting in a permanent dog.

Also, dog owners seem to vary just like parents of children do -- there are some houses where visitors have no choice but to sit on the dirty couch and be climbed on, and other houses where one can visit without being drooled on by child or dog if one doesn't want to.