When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The ads are determined by what you have been viewing/searching in your web browser. I notice that if I have done a search on a particular item, all the ads will be for that item I was searching. It is tied in to the cookies on your computer. Therefore, you are seeing GM ads because you have been looking at the GM sites, or some other family member has!