[mothered]

What makes you so sure you have "nothing to lose"?

Because If It's opened, It can be returned for a legit refund by saying you were In a rush, and mistakenly packed the Incorrect Item In the box. As to why It was resealed to perfection, you were concerned that an open/damaged box would void the refund, hence returned It In Its original state.

In my head there are horror scenarios like police investigations etc..

There's no cause for concern - they're both part of company protocol to move forward with the claim.

So I could take a big stone that has the same weight?

No, replace It with an actual product.