Paid Review Ethics

I know a lot of people are into blogging simply because they  want to make money out of it whether be it from ReviewMe, Blogvertise or PayPerPost or from any other blog paying site.  There's nothing wrong with this if one can earn a few dollars on the side while doing what they love to do.  But how far should one go if the question of ethics is taken into consideration. 

Advertsisers  such as those I mentioned offer bloggers money for marketing review and PR messages. Doesn't matter if its a positive or a negative review since it offers  advertisers an expanded  market niche from a lot of readers. Bloggers meanwhile take advantage   since they are being paid for this. 

Bloggers have the responsibility to inform the readers the truth and not just write an article for the sake of earning.    So the question is to write a paid review or not?  In my opinion, you should tell your readers that you have been paid for the review and try to make a truthful and balanced review rather than making an effort to sell what you may not necessarily believe in.