|Selling Ashes of Al'ar and Twilight Drakes|
These beautiful mounts have lots of demand available!
This method focuses on bringing a person with you to a Tempest Keep or Obsidian Sanctum mount run, and should a mount drop, the person pays for it. This method has quite a bit of demand still, as people can't fly in Draenor, but want to use eye-catching ground mounts. Flying mounts can be used as ground mounts now, and there are some very exotic choices.
Here's all you need to know about both of these instances and how to get the mounts:
Tempest Keep - The Eye (Ashes of A'lar, low drop):
Obsidian Sanctum (Twilight Drake, 25 player HC, 100% drop):
As for the payment, in the case of a guaranteed drop, like Reins of the Twilight Drake from Obsidian Sanctum you don't need to ask for any upfront payment. Just use master looter setting and assign the mount to the buyer once payment is done. Keep in mind that you have to kill Sartharion before killing any of the minibosses. Trash can be cleared first, but it's not necessary if you AOE (Just avoid killing the minibosses). Players should be level 80+ for this raid.
In case of a non-guaranteed drop, like Ashes of Al'ar, you should ask for a small upfront payment for your time, perhaps 10% of the total sum, and rest if mount drops. Also make sure the player is level 70+.
How much you want to charge per run is for you to decide. The latest nerfs made all these instances soloable by all classes, so they are incredibly easy now even in 25 HC setting. But don't tell this to everyone, as only a small part of players know that, and that's how you make your wow gold.
I usually ask a player to give their offer, and if it's decent (A few thousand is enough for me, but have made even 40k per drake a few times), I accept the offer and do the run for them. Then I can log onto an alt and repeat the process. Keep in mind that you can sell only one run per week per character.
To spice things up nicely, you can tell people that they will get ALL the loot. Like a Tempest Keep Eye run often gives loot worth a few hundred wow gold. TBC raids can also drop incredibly valuable transmog items, so it's possible that they will earn tens of thousands gold from the run + get the chance for a mount.
So in this case a small upfront payment could be in order, and use the Free for All loot setting, except for Kael'thas you should use Master Looter.
Example advertising texts could look like this:
/2 WTS [Ashes of Al'ar] Mount Run! ALL drops are yours, including mount, pets and valuable transmog items like Blade of Wizardry that go for tens of thousands gold! (Level 70+)
/2 WTS [Reins of the Twilight Drake]! Beautiful Flying Mount! Fast mount run, guaranteed drop! (Level 80+)
You can get clickable ingame links from wowhead.