I had one failure and one success at fostering....
I have one cat that has tested positive for FIP and so I should not foster until all my cats have passed on.
I found a kitten in the road a couple of months ago and kept him for a couple of days until I forced him on a co-worker. I kept the kitten in a different room and didn't let contact happen. I didn't want him to be exposed to the FIP thing.
So, I would never volunteer to foster, but in a pinch, I can do it.
I don't think I could ever turn down a little one, but I do feel responsible enough to keep it from my four cats.........
I could never foster if I had not been discovered to have an FIP cat. I would keep them all - for a good example....Lucy the little barn cat is now part of my four.
:D