One of my students told me a story about his wife. She was thinking about going to cosmetology school, and had been researching online. He got a call from her the next day, because she had been on Facebook and an ad for cosmetology school had popped up.

“It’s a sign!” she said.

Actually, it was behavioral targeting. When you travel around the internet, advertisers, including Google, notice where you’ve been and what you’ve been looking at. They figure you’re interested in that stuff, so they show you more of it.

We’ve had clients upset because they go to Facebook and see ads for their competitors. Sometimes they figure we have done that. In fact, they’ve done it themselves — or allowed Facebook to do it.

Aside from questions like, “How come I’m seeing these ads?” we also get questions like these:

• Can I control the ads visitors see? On your own website, if you have set up Adsense ads, you can specify some parameters. You can list specific URLs you don’t want to allow, block categories (both general categories like Apparel and “Sensitive Categories” such as black magic, get rich quick schemes, and video games). You can’t, however, make up your own rules, like “Only Republican political ads.”

• Can I make my ad show up on particular websites? If you want your ad to show on a particular website — and that can certainly be a good way to go — you should just arrange it with the website in question. Ads served by Google or another ad website might turn up there, but it’s more efficient to ask for a banner ad. “Banner” can mean the space at the top of the website or it can mean a smaller ad in a sidebar. These ads are usually charged by the month, not by the click, so you’re paying for the space rather than on the basis of the ad’s performance. Expect to pay anywhere from $50 to $5,000 depending on traffic to the site, ad size, and competition for the space.
• Does this creep people out? People considering using this type of ad often wonder how many people repond badly to ads like this. The truth is, people who don’t understand how these ads are triggered often don’t even notice it. Ads for things they like show up in languages they speak, so there’s nothing to alarm them. For many people, it’s a lot like having a helpful sales associate in a store come up and say, “We just got this in and I know you’ve been looking for one” — that is, it’s perceived as helpful. People who are really bothered by behavioral targeting can block these ads.