There is a 4.5 player on my team that footfaults on every single serve. He kinda shuffles both feet forwards a bit as he tosses the ball, and ends up with his front foot maybe an inch on the line. And does this consistently - it's part of his service motion.
We've pointed it out to him, but I don't think he can fix it - it's just part of his serve. The only thing he can do is start off a couple of inches behind the line. When we remind him he does that, but then he forgets and reverts back to footfaulting.
Of course it's against the rules... but he gains absolutely no advantage by doing this. He's never been called on it by opponents. Actually I would be very suspicious if opponents ever called it on him - I don't think you can conclusively say that he is footfaulting when you are looking from across the net.
But if we were ever to play with linespeople and they called it on him that would be justified since it is obvious when you are looking from across the baseline.