I am trying to withdraw a single scrap but for some reason instead of handing me the scrap in the trade window dispenser 11 would rather spam me with "Shop overloaded! You can only deposit 0 items!" every 1 second, even though I am not trying to give anything to him, just take. Thanks.

In your case, you have to take 2 items out and put 1 in. It is some kind of inventory limit counting bug since people are bypassing the limit with bag trade.