Even if you provide your so called vouch's for free..No one will trust you dude coz you are a newbee..People hardly trust them..Vouches should be provided by Sr member + so that others can trust..Believe me if you provide any vouch for anything,people will think you are doing that for some btc's so please lock this thread and first become high level member before providing such service 
With regards to ebooks, it's obvious as ebook copies are only given to trusted members. However, there are many people who require users to test their games, apps or software which is useful to them as OP gives them a review for free. No harm i trusting OP in this case if he can provide a genuine review with proof that he has tried to website/game.