[mothered]

Let's say a box of Pokémon cards <100euros. Like an ETB or better.

If you hit them during the busy time of year (towards Christmas), any company on a medium to large scale will be Inundated with orders and claims, therefore won't have the manpower to thoroughly check each and every one.

Moreover, It's a low value Item, hence the cost of Investigating the matter will outweigh the cost of the Item.
Do you happen to know Its precise weight?