Never have I tryed anything quite like it
When you want to sell traffic to them:
They test your traffic and value it for you.
They sell the traffic for what it's worth!!
I sell traffic from a 50% skim TGP to average $2.39/k and I know of some qaulity sites selling to $2.9/k.
When you want to buy traffic:
they give an estimate on the prod of the traffic and that is typically in the low end of the truth!
I bought some feeder traffic for my site and it was of course awesome because it's tested and you know exactly what you buy!
I just almost doubled my earnings by starting selling to trafficholder instead of a certain other traffic broker.
www.TrafficHolder.com 
This is the place to sell and buy traffic if you don't want bad surprises.
This thread is a bit spam alike but I am just so fucking impressed with these guys since I tried for ages to find a good traffic broker