This is sent by the client to buy items from a vendor. This is sent by the server to remove the list.

Offset Type     Name             Description
------ -------- ---------------- ------------------------------
 0000  cmd
 0001  USHORT   blockSize
 0003  UINT     vendorID
 0007  BYTE     numItems         Setting this to zero will remove the gump.
       for each item
       {
       BYTE     layer            usually 0x1A
       UINT     itemID           from 3C packet
       USHORT   amount           # bought
       }