In the US, if you use affiliate links on your website, you’re required by the FTC (Federal Trade Commission) to disclose this.
Back in 2009, the FTC started releasing guidelines for websites that use affiliate links. These guidelines and the affiliate disclosure requirement are an attempt by the FTC to protect consumers by letting them know that any endorsements or product recommendations they’re relying on come with a potential financial gain to the website doing the recommending and endorsing.
I’m and Affiliate marketer with links to an online retailer on my website. When people read what I have written about a particular product and then click on those links and buy something from the retailer. I earn a commission from the retailer.