There are some official guidelines regarding affiliate marketing, notably that you must disclose that you are compensated for providing reviews.
Thanks to Amy Lynn Andrews of The Useletter® for an excellent post regarding disclosing affiliate links. Her article neatly summarizes much of the official FTC guidelines below.
Official FTC Guidelines
Native Advertising Guidelines:
.com Disclosures [PDF] (Appendix includes 17 Examples)
FTC Guidelines on Social Media via their FAQ on What People Are Asking: