Most advertisers spend hours thinking about what they want to target. Smart advertisers spend just as much time thinking about what they don't want.
What is a Negative Keyword? It is a flag that tells Google: "If a user uses this word, do not show my ad."
Why it matters: If you sell "Luxury Software" ($500/month) and you don't add "free" as a negative keyword, your ad will show for "Free Software." You will pay $10 for a click from a teenager who has zero intention of buying.
Before you even launch, copy-paste these lists into your Negative Keyword List. Unless you specifically offer these things, they are budget killers.
The "Freebie" Seekers: free, cheap, download, torrent, crack, hack, open source.
The "Job" Hunters: jobs, career, hiring, internship, resume, salary, training. (If you don't block these, people looking for a job at your company will click your ads instead of visiting your "Careers" page).
The "Do-It-Yourself" Crowd: how to, diy, tutorial, guide, definition, what is, wiki. (These people want information, not a product).
You can't guess every bad word. You have to look at the data.
Go to Keywords > Search Terms.
This report shows exactly what people typed into Google to trigger your ad (not just the keywords you bid on).
Sort by Cost.
Look for irrelevant terms.
Example: You sell "Office Furniture," but you see you spent $50 on "Office Space for Rent."
Check the box next to "Rent" and click "Add as Negative Keyword."
Pro Habit: Do this once a week. It is the single fastest way to lower your CPA (Cost Per Acquisition).a
It is important to understand the difference between a Negative Keyword and ClickSambo.
Negative Keywords block Bad Intent. (e.g., A real human who wants something "Free").
ClickSambo blocks Bad Actors. (e.g., A bot or competitor who clicks your "High Intent" keyword repeatedly).
The Strategy: You need both. If you have a great Negative Keyword list, you ensure your ads only show to "Buyers." If you have ClickSambo, you ensure those "Buyers" are actually humans, not bots draining your budget.