I really don't think you can be 100% positive they're gone with cats or dogs. My poodle is white and when I bathe her, you can really see her light pink skin and any black fleas on her. Every time I bathed her in the summer (flea) months I would find anywhere from 10-20 fleas on her. I'd take them off and kill them (just putting them in a small drop of dog shampoo that I squirt on a plate does the trick), then I'd double check everywhere on Gigi to make sure I got them all. When I think I have and start to dry her, sure enough 2-3 more fleas would be on her. Argh! It is really frustrating, right? And even when you do get them off, you take the chance that they will jump back on from going outside again or from even just being in your home.
Every summer we have to apply Advantage to our 3 cats and 1 dog and flea bomb the whole house. I just look at it as a given each summer that we will have to deal with it. Even though all our pets are indoor pets, humans can bring in fleas from working in the yard.