When you promote a product you also promote the person or the company who is behind the product so try to choose wisely. You don’t want your visitors to go and buy a product following your advice then come back unhappy. Do you think that this visitor will come back to your site and take your advice again? Most likely no; this can hurt your credibility in the long run. Usually, websites/company that offer good customer service will have better customer satisfaction so try to stick with promoting their products.
For example, I have a post featuring 10 Affordable Headboards on my blog. Now, instead of just pinning the “pinnable graphic” you see below, I pin that PLUS individual images of each headboard featured within the post. That exponentially increases the chance that people will click on the pin and through to my blog post, which in turn increases my chance of making affiliate sales from that post. Plus, it also boosts traffic to that post, which translates to more ad revenue as well–it’s a win-win!
Some commentators originally suggested that affiliate links work best in the context of the information contained within the website itself. For instance, if a website contains information pertaining to publishing a website, an affiliate link leading to a merchant's internet service provider (ISP) within that website's content would be appropriate. If a website contains information pertaining to sports, an affiliate link leading to a sporting goods website may work well within the context of the articles and information about sports. The goal, in this case, is to publish quality information on the website and provide context-oriented links to related merchant's websites.
While there’s probably a part of luck, the way you present yourself also counts. I just corrected a bunch of mistakes in your comment before approving it and I can imagine if your email to Amazon looked the same, they did not take you seriously. Consider using the free version of Grammarly when you write online. That will do a lot for your credibility (and that’s coming from a non-native speaker that also makes a bunch of mistakes and has to spellcheck a lot of what he writes).