How do I make an optional dialog give the player an item?

So I made an npc that acts like a merchant and I have a couple dialog choices. One has the player not being interested in the item. The other has the player act like they are buying the item.

I made the item but I'm not sure how to give it to the player if they choose that dialog option since this is not a quest dialog. Is what I am trying to accomplish even possible or do I have to turn it into a quest? I don't want to force the player to buy the object though.