I was visiting the website of a local confectionery when I noticed something strange at the top of the page. You see that? It's not just an ad, but it's about type 2 diabetes - the kind you can get from eating too many sweet things.
Why on earth would a bakery want, or even allow an ad that seems to cast its products in a bad light? The problem seems obvious at first; the ads are context-based. That means some keywords on the site matched up with some ads in the service's system and there you have it. Sugary food gets us diabeetus. But most site owners would prefer to keep certain ads from their pages because of undesireable associations such as, I don't know, their products might give you a disease.
Then I noticed something else. That URL in the location bar isn't for the shop in question. It's for a mobile website service, DudaMobile. This is the real problem with our scenario.
DudaMobile makes money in one of two ways: either you subscribe with a monthly fee (discounted if you pay annually), or sell ad space at the top of your website. I don't think every website faces such comically mismatched ads, but it's the price of "free" in this case.