Not being able to buy single items from a stack on the marketward.

[Jinko]

It makes it a lot hard for RMT to take over the markets for items that become valuable.

That's probably the number 1 reason they did this. The little Janes that need items have a lot more purchasing power but need smaller stacks. There are few people who truly need 99 of anything that wouldn't just go out and farm what they needed instead of spending gil. This system is a huge blow to RMT.

It also prevents people from stockpiling things and then flooding the market with them, driving down prices. And it keeps undercutters from annoying the living daylights out of everyone.

This system is very very stable.

You bring up some valid points as usual.

Suggestion 1

Would it not make more sense to only sell items per 1 or stacks of 12 like in FFXI then ?, it would make it both more competitive and stable.

Forcing smaller stacks would also mean you could fit less items in your retainer sales interface stopping people from flooding the market.

Suggestion 2

How about giving sellers better functionality to sell stacks of items, for example a drop down box to quickly set stacks ranging from 1,10,20,40,99, I am all for compromise.