As a makeup artist I can honestly say that I have received free products that I've absolutely positively HATED...It being free doesn't make me like it and it doesn't persuade me to like it.
The free stuff I've been given that I don't like, I either give away or give it to my 6 year old daughter to play with.
I don't do youtube videos but I can totally understand why a Youtuber would review only products they like...why waste time on saying, "oh I hated this it sucked" Some of the YTers like Panacea81 ( I think I spelled that right) have a massive following...Could you imagine what would happen if she totally ripped on a product she received from a small company? It could potentially cause real harm to that very small company's financial system.
I can totally understand why "gurus" would review the same product. Each guru has their own unique audience and followers. People value opinions of different people. There are a few YTers who I wouldn't take skincare/makeup/product advice from if my life depended on it...There are others who I feel hit the nail on the head most of the time. If a guru has tried a product and feels it's a great product why wouldn't they do a review on it? Sigma brushes for example...Being a makeup artist brushes are probably the 2nd most important thing to me...I was pretty damn skeptical about these brushes until I saw a review from a guru I really like. I am a MAC brush girl all the way...i bit the bullet and ordered a few sets of these brushes after reading/watching a few reviews and I have to say, I love these damn brushes. I saw a few people on other boards say that a certain YTer who promoted sigma hardcore, didn't use the brushes very often in her tutorials,so they found it hard to believe the brushes were good...To me this wasn't a very valid point. As much as I love the sigma brushes, I almost always reach for a MAC brush first. It's habit and I have so damn many MAC brushes there are almost always a full clean set laying around and just because a product is really good doesn't mean someone will use it all the time...While I love sigma, MAC will probably always be my first choice. Same can go for eye shadows, foundations, lipsticks, etc. I think you have to take all opinions and things like that for what they are worth and just jump in there and try the products for yourself. Everyone has different tastes and no one is forcing anyone to buy anything.
I just don't understand why people find the redundancy of reviews obnoxious. Like I said earlier, each guru has their own audience...So it only makes sense for each guru to review the same products as other gurus, especially if they really like the product and want their audience to know. Hell if you even read in the comments for some videos there are people asking that specific guru to do reviews on certain products that have been reviewed by other YTers already.
Food for thought...why would a popular YTer give a good review to an item they honestly thought was crap? Wouldn't that be risking a lot for them as far as the Youtube universe goes? They are potentially risking losing loyal fans and subscribers and people would stop taking them seriously. So, in my opinion I don't think it's very likely for the bigger, well known YTers to give false and shady reviews for products they truly know are crap, it just doesn't make logical sense. They may get more free stuff for while but that will eventually die off because their audience will shrink and no one will be offering someone with next to no audience free products to review/promote.