As of December 1st, 2009, you must disclose on your website or blog if you are being compensated for endorsing a product or service. Also if you are an affiliate of the company selling the product. That’s the gist of what I’ve uncovered by doing a little research.
There’s a lot of information to be had online, from penalties to legal documents sold to post on your site. I am not a lawyer, but I doubt you will get penalized if you have a link to an Amazon product on your blog and you neglect to mention that you are an affiliate of Amazon.
As with graphic design and copywriting, if you use someone else’s stuff (images or text), that’s a no-no and you would probably get a “cease and desist” order to stop using it if caught. So please don’t steal someone’s hard work. Create your own instead. It’s much more fun and rewarding.
So if you promote a product or service that you are going to benefit from, it would be nice if you mentioned that. If you’re not being compensate, you could mention that too.
For instance, if you click on this link for ProBlogger, a very helpful and informative book on blogging, and then buy the book, I get a little change. I actually have bought the book and am reading it. And I do recommend it. It has been very helpful in setting up my WordPress blog and when I start earning a six figure income, you will be among the first to know.