Well I've recently come up with a strategy for crafting in the crafting Guild.
Ive buy soft clay from GE and equip a brown apron, Ring of Dueling and the Clan Vexillum.
1.Start off in the bank with equipped items and fill inventory with soft clay.
2.Teleport to the clan area with the Vex and go over to the crafting guild.
3.Spin what pottery your going to make.
4. Then go to the other side of the room and fire it.
5.When done use the ring of dueling to teleport to Castle Wars.
6. Deposit and repeat.
Strong Cooking Urns(Level 51) sell for 419+ each Always try asking for more then market first.
Other strong urns you can make a profit on but as far as I know that's what sells for a good price.
Good Luck and I hope this helps