Whenever someone is penalized, point them to the specific rules they violated. And keep in mind that people make mistakes every now and then. Show largesse. This isn't a production line where flawed products are tossed out at the blink of an eye.
Last, don't view everything as a "problem" to be "solved". We're talking about human beings, not Turing-complete automatons. That's a big part of the problem with how HN is run. You will never "solve" this the way you would a bug.
You need a human element to address something human. Treating everyone like a spam bot only works for spam bots, and has the side effect of pissing off the human false positives.