From what I understand, at least with CW consignment, you tell them what you need out of it. They will put a higher price to make their money. It may be 5% or 25%. But I never heard there was a percentage. A coworker sold his through last year. From what he told them he needed and what they listed it was less than a 10% difference.
If you sell it on your own, then you need to market it on your own and be available to show it to everyone that says they are interested. If you have a lien on it, then your buyer gives you the money and you turn around and pay off the lien. The lien holder will then release the title, which the purchaser will need to register it. The state will then do new title paperwork and will either send he title to the owner if paid in full without a new lien, or they will send it to the new lien holder.
Having it consigned takes a lot of the work and headache out of it. Yes, you may not get as much as if you wait it out and wait for the right buyer, but if you are looking to get rid of it faster, then I would go consignment.