[mothered]

But, when they discover it’s a fake one, the can refuse the rufound request, right?

They don’t check the item, before to send the refound?

Yes they do, hence:

Simply return another stock Item, that weighs roughly the same.

You're not following. You do not send a fake Item.
Here's a breakdown.

(1). Purchase "another Item" that they stock, Is significantly cheaper and weighs roughly the same as the watch.

(2). On request, send the "other Item" that you've purchased.

(3). They will check that It's part of their Inventory, and assume they've sent you a wrong Item.

(4). They'll then Issue a refund on the watch.