But your not saying that the work you did was a proper fix. You attempted a repair and performed work. We can use the car analogy.
My car is sputtering and acting up, so I take it to the shop and have them look at it. They do some work, and while it seems to have gotten better for a while it starts to act up again. I take it back, and they find more problems with the car. They fix the problems and charge me again. They may offer a slight discount (especially if I raise a stink) because the first repair didn't fully solve my problems.
So he brings in a laptop that you do a virus clean up on, and a tune up. That may or may not fix his issue, but if it doesn't... you've still got time invested into that cleanup in an attempt to fix the problem. Because you honestly felt that the cleanup/tuneup would solve the issue. There is no reason not to get paid for that service. You can (and I would) offer them a discount but as I've said you need to be reasonable to yourself as well.
Now if he came in with the problems you describe, and you install a new CMOS battery and keyboard and send him on his way..... then yes you've now charged for parts and labor that you should not have and you knew they wouldn't solve his problem.
