I think 12 is fine.. 99 would be too much for some items.. and make it more difficult to sell on the AH

One example is its hard to sell geodes on the AH as is because you either sell them one at a time or wait forever to make a stack of 99

My AH slots are valuable.. i can't afford to sell one thing at a time >_<

an option to sell 12 or 99 would be nice but i'm not sure if that is even possible.