I think some of us were expecting it T_T (Possible Xmas hill exploit + rollback)

Are you telling me they didn't make a check to make sure people don't put in a negative number? REALLY?

There is a check for normal shops, just not the flakes store although it is sent via the same packet header.
It goes something like that :

<2 bytes header>
<1 byte mode> // 0 = Buy, 1 = Sell and so on
<2 bytes 00 00> // This is probably to determine if the item is sold in meso, or with item
<4 bytes itemid>
<2 bytes quantity>