1. Unlike positive keywords, negative keywords need to be built out for plural terms and different word forms. For example, in AdWords and Bing, a negative keyword -car will not exclude searches with “cars”. The negative keyword -DIY won’t exclude searches including “do it yourself”, and the negative keyword -repair won’t exclude searches with “repairing”, “repaired,” or “repairmen.”
2. When building out negative keywords, be sure to eliminate searches for irrelevant services outside of your industry. For example, home window installers need to protect themselves against searches related to Microsoft windows and car windows, and cabinet companies need hundreds of terms related to the President’s cabinet. Even a product as esoteric as industrial plastic extruders needs negative keywords like pasta, noodle, and fruit so that you’re not wasting thousands of dollars on searches for kitchen appliances.
3. Negative keyword lists need to be regularly monitored and updated. This is the best way to prepare against queries that are surprising or very recent. For example, one company selling CAT industrial pumps was hit for thousands of dollars of searches on Hello Kitty heel pumps. (By default, positive broad match keywords will treat “CAT” and “kitty” as synonyms unless you tell Google otherwise). In another case, one of our North Carolina bathroom remodeling clients had an increase in irrelevant searches after the state proposed a state law around bathrooms. Addressing these issues is very easy if clicks are regularly being audited (e.g. adding “law” and “legislation” as negative keywords).
4. We generally recommend having hundreds or thousands of negative keywords for each campaign. About 25% of the new clients that we speak to had 0-20 negative keywords before signing on, a serious problem that generally would cause about 10-20% of your budget to get misspent on irrelevant searches rather than on generating income for you. If you don’t already have hundreds of negative keywords, this is a major opportunity for increasing the revenue you’re generating from your current budget.