SEO only works for your own website as you can edit the keyword in the meta tags yourself. It is most important to think about your keywords carefully as it is crucial for your ranking at search engines. If you do this right you can get a lot of traffic for free.

When you are an affiliate and using a provided website with your code in it, you can't use SEO.

PPC at Google and other large sites can be a costly affair if you want to get a lot of traffic. It certainly brings in a lot of visitors, however you don't have any guarantee these visitors will make a sale or join your program.
Google requires you add the abbreviation "aff" in your ad when you are promoting an affiliate link.

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