Rpg Maker Developers Group

So, thanks to this helpful other thread: http://forums.rpgmakerweb.com/index.php?/topic/18927-need-help-with-using-items-at-specific-times/ I figured out to make my player choose an item at specific times I need to use the Select Key Item command. I have set up the variables, my only problem is connecting the item to the variables. What I want is for the player to purchase an item from the shop, and present it to an NPC to get a reaction. How can I set up Shop processing so that when the player purchases the specific item, the variable I set up is also increased to 1 for the purpose of later using the select key item command to check that the player has selected it? I have several possible items the player can purchase, so how can I ensure that only THAT specific item increases the variable? Thank you a lot for any advice you can offer me! Apologies if this is at all in the wrong section!

On the request of another, I'll post these screenshots that will hopefully give you a better idea what my problem is. Thanks much everyone who has answered so far for your help!

The first on is of the Key Item Select event, I have the 4th variable set to 013, the i believe, ID of my item, Bat Doll.

The second is a screenshot of the actual event page. I'm actually having trouble getting it to work properly, if anyone could help me out with that, I'd be very thankful. What I want is to give the player the option to give multiple things which are viable, but only one of those three things will result in a point towards another variable I have set up, the girls' love interests.

Finally, the third is of my item screen in  my database, to give you an idea what the items are assigned to which IDs. 

Thanks for all your help! Especially Shaz whom has replied on multiple threads of mine and seems to be a very helpful member of the community!

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