In regards to the above questions about redirects and products:
I don't think google allows page redirects any longer. Or rather, the domain you list on your ad must match your destination page. So if a merchant does not allow you to display their url, you can't redirect through your own page.
What I was actually talking about, and what I've had some success doing is create an actual "storefront" for products. To continue with the camera example...
I'd find a merchant that had a datafeed with cameras. I'd make a *complete* site with cameras for sale. So I might have a left menu with different camera brands, and on each brand page have that cameras product families, and finally down to single products. The click from the product takes them through my redirect system and then to the merchants buy page. So it would be something like this:
menu:
canon
kodak
olympus
when a user clicks on canon, they are taken to an insite landing page for different canon camera families.
canon->
rebel
powershot
etc.
Now there are two ways to do this - list every single model for a given product family on this page, i.e.
rebel
rebel model1
rebel model2
rebel model3
powershot
powershot model1
powershot model2
powershot model3
or have links that take the user to a page dedicated to that product family
rebel -> rebel.html
powershot -> powershot.html
Finally, when a user clicks on a specific model, they are taken either to a) my redirect system and then to the merchants selling page or b) my own selling page which has links to the merchants buy page.
By doing this, I also get a natural seperation of landing pages for keyword terms. For my keywords that have to do with digital cameras, I take them to the home page with ALL cameras. Then I break it down by brand - canon camera keywords take them to the canon product family page. Then, by product family - rebel keywords take them to the rebel product family page. And finally, by specific product number - rebel model xxx takes them to the rebel model xxx page.
Now, I don't know that I'd suggest this approach unless you have some programming savy, because it is very labor intensive otherwise. Plus, you'll want to track which keywords are actually converting from which ads, which you can do through your own redirect system. Whenever a user clicks a link that leads to a merchant page, insert the keyword that got them to your page, the model they are clicking to, and add a subid to your aff link so you can track sales according to model numbers.