I definitely DO NOT want to see the ability to purchase single items from a stack of 99. If that is incorporated, everyone will be selling stacks of 99 and the only way one could sell anything would be to undercut the lowest price. The undercutting would continue until there was no way to make any money.
As it now stands you can buy from people selling smaller amounts and although the single item price may be slightly higher, the overall price is much lower. Or, if you don't like that, go gather. After all, that's what this game is all about.