Selling on consignment can be an absolutely great deal for shops, under the right conditions.
If I'm a lego trader and I buy your set for $900 hoping to sell it later for $1000, in the meantime that's $900 I can't invest in anything else. And maybe I guessed the set's value wrong and I end up unloading it for $800, taking a loss.
On the other hand, if I agree to sell that same set on consignment? Zero capital outlay, zero risk of me taking a loss - just some shelf space and admin work.
Much better deal for a diamond ring than a giant kayak, then. Gotta pay rent to sit on the shelf!
> just some shelf space
Unless the store owns its building and has too little inventory to cover the shelves, the cost of not filling the shelves with the right goods is quite serious. In a low-margin business like retail, "just some shelf space" reads almost like "just some gold bars".