Google has a rule which restricts affiliate marketers to one search query spot for each top level (display) domain. This has implications for affiliate advertisers that run their content on a shared or large website where other affiliate advertisers may be present.
Google will determine that these websites will be the same and will only permit one query spot for these addresses:
However, these domains are not equivalent in Google's "eyes:"
Another rule that affiliate advertisers should abide by is that your website should not mirror or duplicate another website. Google will not show ads for identical websites. Their goal is to provide unique and useful content to users and they view such duplicate material as not useful.
By the way: If there are two duplicate websites, but one of those websites ranks higher with Ad Rank, the higher ranking site will most certainly win the contest. This rule assumes that the two website landing pages are not violating other rules for affiliate ads or regular search ranking that would cause penalties.
In essence, even affiliate advertising requires unique content for the contest of organic search query results.