MOST OF THE DEALS ARE CAN ONLY BOUGHT BY BITCOIN !!!!!!!!!
I've never checked out dark web, but I'll use some common sense / logic. There are more directions here:
1. I expect that some of those "deals" are fake, like everywhere in the world. So obviously a mean of payment that's not reversible is preferred by the sellers.
2. Since the things sold/bought there are usually (?) illegal, linking them to somebody's name, address, face.. are clearly avoided.
And then the next question arise: how comes they don't use anonymous coins and risk (just a little, I know) to use Bitcoin?
I hate to say this, but you are wrong. Deep web is the place where all of the things are true, the Government's secrets are even there, lots of confidential and unimaginable things you can't picture out in your mind. Deep web is just a mask, the most interesting things are inside. All of the deals and transactions there are legit, because the word "respect" are valued there, unlike here in the internet (you know what I mean).
They respect each other because not all of the people have guts on diving down in the deep part of the web yet there are some, and that's what I like about in deep web, their system and the people.