One thing to be aware of is this.
If GD reduces the commission to 9%, chances are they will increase the price upstream to cover the difference. And that's actually for a reason that can be deemed valid (I'll let everyone decide but let me explain below).
The above means, your end price sale will likely be higher and as a consequence sales will be lower. So the 9% fee will not bring more money to you.
Edit: Dan uses your own lander traffic to sell the domain. While you can sell a lot through Afternic even if you point landers at Dan. Which means Afternic brings the bacon themselves and that's at a premium.
As you might know already, the partner network of Afternic practices a markup price as they desire. I've had domains that were priced 50% more in end retail price of given platforms. It is most likely the decision of that partner platform how to price. But I would bet that the difference will be passed on to partners as retail price at Afternic's gate.
There is, however, a business reason for the 20%.
While Afternic has to make their own money, there are also partners there who sell your name at the same price, or even for lower price. Yes, even a bit lower sometimes than Afternic (your) price.
For these partners, the payout comes from that 20% of course. So overall I bet Afternic keeps a portion for them (say 10%) and offers the other say 10% to the partners that bring this exposure. And those who sell at lower prices have a better chance to sell names.
In other words, with Afternic you get a ton of exposure, but it comes as a cost - partners have to eat too. Hence the 20% fee.
Edit: Also please remember Afternic has people that can answer calls. For certain domainers this might be vital. I am one of them; NS5/NS6 landers work far better for me in comparison with Dan where I never got good results. But this on-call team also comes at a cost. They also offer account managers like I have that is extremely helpful with any issues with listings and everything else. Yet more reasons why a higher fee is basically expected with Afternic/ GD.