ANSWER - The key to answering this question of course is whether or not Karma actually exists. Karma is traditionally an Eastern concept and one which many practitioners of witchcraft, particularly those in the West and particularly those who not subscribe to the New Age ideas of magic do not accept as part of their belief structure.
The principle of Karma - as I am sure you are aware - is that people receive back what they put into the world. The idea is that good begets good and evil begets evil. This view can be adopted as a general belief or in some cases it is accepted as a quantifiable principle with the idea that specific deeds are measurable in terms of their good/bad nature and then the same precise amount of good/bad is returned to them as a consequence of their actions. Wiccans especially tend to be quite keen on Karma - think the threefold law of return.
My own personal path doesn't incorporate the idea of Karma much beyond the idea that if you go around being nice to other people chances are that other people are going to be nice to you. There are too many issues with the undeserving being rewarded or the suffering of good people to substantiate a Karmic world view in my opinion. This imbalance is often addressed by supporters of Karma with the argument that the rewards and consequences of our behaviour can trangress different lifetimes. But I would argue - firstly there is no proof for this and secondly for those who believe in reincarnation the idea is that we get a new chance each lifetime to take a step closer to our full potential as a human soul and it simply makes no sense to carry the baggage from one lifetime into another.
The concept of good and evil in the Karmic view is also too simplistic for my liking. People often do bad things for a good reason and good things for a bad reason. Nor is there a universal agreement on what exactly defines good or evil. For Karma to work there would have to be an absolute source of moral authority. This could possibly be substantiated in a belief system that yields to an omniscient deity but it is shaky ground and smacks more of Pavlov's dog mentality that it does morality. If we only learn morality through punishment for our actions then it could be argued Karmic morality isn't morality at all - it is simply learned behaviour.
There is a certain amount of idealism in people wanting a world where everybody gets what he or she deserves but the truth of the matter is that as long as human beings have free will there will be inequality between those receiving reward and those receiving suffering. It is hard to reconcile the idea of free will with the concept of Karma.
Coincidence is also a big issue when discussing Karma. In an average lifetime any person will go through many good and bad times. They will undertake both good and bad acts and both good and bad things will happen to them. It is easy to find a pattern if you want to look for one but the fact that a good action is undertaken and is followed by a positive consequence is not evidence of cause and effect.
So I may not have been the right person to ask about Karma - if I'm completely honest it doesn't grab me on either an instinctive or an intellectual level. I don't believe good and evil can be neatly defined and labelled and I don't believe the world operates on the principle of "fair" which is essentially what Karma is I think to say that those who suffer deserve it on some level is both wrong and naively simplistic.
I don't speak for all witches of course but I think you will find a lot of witches who practise Trad Craft will agree that there is no universal balancing of the scales to punish or reward. Sometimes the good go unrewarded and the evil go unpunished and that - as they say - is that.