I really admire people who can foster a dog. I don't think I could do it, to start to love a dog and then let it go to someone else. I would always be worrying if it was OK! I have a friend who does the puppy stage of guide dog training, all the hard work and bonding, then for it to go to it's new (blind) owner. What courage.
Having said that, now I am getting quite old, I think after Dylan I might not have the length of life for another dog, let alone the now astronomical vet fees, so maybe fostering would be a good idea for someone in that position. Tricky.