
If you don't think retail sites like Amazon.com and Walmart are search engines, THINK AGAIN! They attract a lot of shoppers (I mean...A LOT) who are searching for a lot of stuff. Retail sites tend to attract people who are further along on the purchase continuum than search engines. That is, they've got their wallet out and their credit card in hand. And did I mention the top retail sites attract A LOT of people?
According to this post on Compete.com's blog, Amazon.com averaged 67 million unique shoppers per month for the first ten months of 2009 (just over twice the monthly visitors of Walmart.com)
So why am I bringing this up at all? Well, as it turns out, many top retail sites sell advertising space and that includes both Amazon.com and Walmart.com. They were calling this "point of purchase" advertising at Ad:Tech last year. I love that shiny new buzzword smell, don't you?
Amazon offers two cost per click programs for potential advertisers.
Here's a summary (gleaned from the above page):

Note you need to obtain approval from Amazon before you can advertise products in Beautify, Jewelry/Watches or Shoes. Your business must also be based in the US (or have a US-based billing address). Each category contains subcategories - to see the entire list, visit Amazon.com. Amazon has provided a handy visual guide to its product advertising program.

It seems pretty straightforward, no? I'm actually a little fuzzy on where Amazon places these product ads. Amazon provides this, rather vague, explanation:
"If you have products which are not currently available on Amazon, we will use the product details you provide to create a new product page. These products will be available in search, browse and on related product pages. If your products are the same or similar to existing products on Amazon, we will display your ads on existing product pages targeting customers who are looking for products like yours."
Okay...so...the ads appear on the product results pages and Amazon will create these pages if you sell something they don't - which definitely feels very search-engine-ish to me even though you can't target your ads by keyword.
It appears that if your product falls into one of the above categories, it should be fairly straightforward to advertise on Amazon. However, if your product is...say...books or music...well you're out of luck. Amazon tries to further clarify what can be advertised by saying, "The items most suitable for the Product Ads by Amazon program are those which require a brand or buying experience not supported by the Amazon shopping cart." They use furniture or customized products as examples.
Product Ad Specs
Advertising products on Amazon requires uploading a feed, just as you would with a shopping engines. Once you sign up for the program, Amazon provides you with an Excel-based template.
Here are the required fields:
Category
Targeting
2. Amazon Clickriver Ads (Advertising for A Service)
a long list of services that Amazon supports listed on Clickriver's site. A few examples of categories include automotive, business, career, children's services, education, events and weddings.
Clickriver Ad Specs