The product already does.
If advertisers can't work it out (and there has been enough written about it and tutorials), then you can be sure they will never get it.
What brings it home to clients is when we show them the traffic the campaigns they set themselves up with receive in terms of clicks, even if they have worked out things like negative keywords.
I find that using exact match, and phrase match normally does the trick, broad might be useful if it's a product name, or the name of a company that can't be confused with anything else, but negatives get added once we start to see stuff in logs. If you saw as many sales that we see transacted when people type in the word "free" you would never use it as a negative keyword again.