If you go to Petalburg, then find the Turtly Leave in the Mayor's front garden. When you have this go to Rougueport and ask Zess.T to cook it. When she has it will be Koopa Tea! Sell it at the shop in Rougueport and you will get a profit of 1 coin than when you just sold it before it was cooked. Also if you do this with mushrooms then you wil get shop points for nothing.