I want to buy an item from a shop, then make shop cast a spell on me

Im making an ORPG and im trying to figure this out. I have a Merchant who sales "Healing services" just a dummy item, dosent do anything. What i want to happen is when you purchase this from him, he casts a healing spell at the target purchasing the item. any suggestions?

Base the Healing services item off healing potion and set "Use Automatically When Acquired" in object editor.

Or sell a rune...

but i wanted the shop (which is a Troll witch doctor) to do the spell animation when he casts, not just buy a pot with auto cast

then you play the cast animation with a trigger.
It's not a big challenge.

I tryed teh method you suggested with making them cast teh effect after the item is bought (auto-use by buying unit) but it never casts the animation for the spell, theres just a green poof from the hero purchasin/using the item, Im moving this to the triggers secion of the board, ty