Reviewing is an easy thing,once you start to know,how to deal with it.For affiliate sites,you got to be more genuine.Otherwise you will lose rep eventually.I know cause am an admin of one year old review site.
As being an affiliate it's not your job to do the heaving lifting of the product, it's the merchants job to close the prospect and sell the product. Don't be afraid to do a negative product review, telling your readers what NOT to buy.You will always make more sales when you can show proof of results. That's why testimonials, case studies etc are so needed.If you can research a lil bit about the product,that you are going to promote,its a definite plus.