For example, if I talk about how cool a product is, and then you find out that I’m an affiliate for them, wouldn’t you as a conscientious observer become skeptical as to whether my information is biased, if perhaps I’m only saying how cool something is because I can get paid for it? Wouldn’t that make you question my integrity with other things I say as well?
I guess the only thing I’d say about this is if you are blogging in a competitive niche and working in what I’d call the “gray area” of link masking and not using “nofollow” as described here by google (https://support.google.com/webmasters/answer/96569?hl=en) expect that competitors that are writing real reviews with real photos (not stuff grabbed from a manufacturers website) are going to report you to google as webspam. The thing I hate most is affiliate sites that have never held a product in their hand and then try to pass off something as a first person review for the sole sake of pushing you to Amazon.com.
In November 1994, CDNow launched its BuyWeb program. CDNow had the idea that music-oriented websites could review or list albums on their pages that their visitors might be interested in purchasing. These websites could also offer a link that would take visitors directly to CDNow to purchase the albums. The idea for remote purchasing originally arose from conversations with music label Geffen Records in the fall of 1994. The management at Geffen wanted to sell its artists' CD's directly from its website but did not want to implement this capability itself. Geffen asked CDNow if it could design a program where CDNow would handle the order fulfillment. Geffen realized that CDNow could link directly from the artist on its website to Geffen's website, bypassing the CDNow home page and going directly to an artist's music page.