If you liked a product, you will always speak well of it. Of course, it is your opinion and nothing more and others will disagree. If they paid you for it, they are sponsoring you and require you to talk about their products. You're reputation is on the stand and it's up to you if you, or anyone getting the same offer, would take such a stand. It's one thing to say you like Coke and you are paid to wear their logo. But if you start saying you like Coke but really drink Pepsi because Coke paid you and doesn't want you to tell anyone; imagine if someone caught you drinking Pepsi after you just said your statement.
You would be ostracized.
If I trusted someone and they were secretly endorcing a product, I would take their word for it without hesitation because I wouldn't know. If it didn't work for me, then I would say I got a lemon. If I find out that they were selling me something and didn't tell me, then I will be the first to get on the air and call foul.
