This is a scenario showing how to put the Buy/Use Potions trick into a scenario. Visit this thread : http://aok.heavengames.com/cgi-bin/aokcgi/display.cgi?action=ct&s=f3nUVzxHXK0i.&f=4,9279,1,10 to see the triggers.
the triggers are a little bit changed, but you can change it another way.
P.S. This only works for One and only One potion. If you want more than one potion in your game...work you brains.