This has gotten me about 30000g in the few months I did it. It's pretty common sense, but more people wouldn't think of it this way, so guide time!
1: Get a group of non-bads (pref. people with the Uld 10 HM drake already, or guildies).
>If 10 man, get 8-9 people
>If 25 man, get 21-22 people
2: Go in trade
WTS Ulduar 10 Man Hard Mode Mounts! <xxxx>g. PST.
xxxx = Any amount, I used to sell them for 5000g/pc to people during the ToC days.
3: You can either explain each fight to them, or if they are terribad DPS, just let them DPS until they die.. On some fights, you can just have them sit out, so they don't whipe the whole raid for failing.
3: Hitup Ulduar, do the hardmodes..
4: ????
5: Make gold!
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You can also do this with ICC 10 mounts, in a few months probably.. Enjoy