A quick summary of how Adsense (the name Google uses for its programme that serves these ads) works, as some people here seem to be unclear about this:
Advertisers sign up with Google and select keywords they think are relevant to their advertising. Essentially they'll try to pick the words that you would type into a Google search box if you were interested in their services/products. For each keyword the advertiser decides the maximum they're willing to pay for clicks on their ad.
Publishers (websites like us) decide where on their pages they're willing to display ads, and their format (size/shape/colours), and put the bit of code there that fetches the ads from Google.
Google sends its spider to pages that display their ads, and decides what they think the content of the page is about. This is similar to their normal search engine spidering, but is specifically looking at pages that will carry their ads.
Google then decides which ads to display when a page is visited. It does this taking into account how relevant it thinks the advertiser's keywords are compared with the page content, how much the advertiser is willing to pay, and where in the world the reader's ISP is. Google then displays the ads it's selected in the box(es) the publisher's provided.
As you can see, we don't decide which ads are displayed or who the advertiser is. In fact we may never even see the same ad as you have, depending on which pages we each view and where in the world our ISPs are located.
This has some incidental advantages, for those concerned about potential conflicts of interest: it's very difficult for us to be conflicted when we don't even know what one of those interests is! The other point is that the Adsense programme is essentially based on "pay per click". With PPC the publisher doesn't get paid just because the ad's been displayed, only if the reader is interested enough in the advertiser's product/service to click on it and go to their website - and if you're reading the Parking Tickets forum here and see an ad for Central Ticketing (say) then you're hardly likely to be interested in their services and click their ad, are you?
What we
can do (and Glacier2 may not be aware of this) is block ads based on their website address, and in fact we block a large number of sites along the lines of www.caughtspeeding-guaranteed2getyouoff.com. If you see an ad for a site that you think is inappropriate or a scam then let us know - if it is then we'll block it.
If you think that an ad is for a scam, for an illegal product or service, or in some other way violates Google's policies then you can also complain to Google. This is potentially more effective, as it could get the advertiser banned completely from Googles' ad programme. Their contact form is at
https://www.google.com/adsense/support/bin/request.py