Regarding “convincing someone to buy your product is not that easy”, I do agree with you, but at the same time, I remember all those products I’ve bought online. I did not search on Google for those products neither I went to the company websites to get information and buy. They were affiliate people and their blogs that inspired to buy them. PrettyLink Pro, SEO Pressor was recommended by Kimberley, I bought Profits Theme, WP Zon builder because Alex Whaley recommended. Similarly I bought CommentLuv Premium because Ileane, Kavita, Steve and many others were talking good about it.
Always disclose your affiliate relationship. Most visitors will probably understand that graphic ads will lead to your getting paid, but if you write a review or use an in-text link as a recommendation, you want your readers to know that may lead to compensation as well. This ensures you retain transparency and trust with your readers, but also, it's required by the FTC's endorsement rules.