I need a little help with my redstone creation

[Matty585]

Sooo...
I have watched this video and came with an idea.
So the idea is that I will have a villager trading farm, and you pay with an iron ingot to trade. Then the system can detect if you entered it right or not.
But, I am having a little bit of trouble getting it to work this way I want it to. (I've been thinking about it for a few days)
The Problem:
The problem is that it how I want it, it will at first mistake any block for an iron ingot, which will then trigger the sticky pistons to trigger, so if you enter any block, they will trigger.

If anyone is a good redstoner, or would like to help me, please leave a post  

[☣2crzy4uall☣]

I wanna help, is it in our map? I think I already know what your issue is!

[Matty585]

I wanna help, is it in our map? I think I already know what your issue is!

Yea, it'll be at the area at my home
Thanks for helping 

[Alec2435]

Why would you want to make this you would still need a player picking up the drops or else they would despawn in 5 min

[jummbocake]

ME! IM READY TO HELP! IM AN EPIC REDSTONER! IGN: plzmyname

[Matty585]

Why would you want to make this you would still need a player picking up the drops or else they would despawn in 5 min

Re-thourght this, I do not need it anymore. I shall use minecarts!! 
If someone could lock this, that would be good 

[jummbocake]

FFUUU