Not a cat owner, so actually curious: I have a friend cat who always scratches me, which is quite painful and leaves marks. Is there a way to trim the nails so this doesn't happen, or is the only solution to avoid the cat?
Normally cats only scratch when you go after them in some way. If that is the case, just don't go after the cat. If the cat goes after you, that's a whole different ball game!
Problems in cat behavior are conquerable, with the right strategies. It seems to be more about changing the environment with cats, rather than training, as it is with dogs.