The law doesn't seem to cover that, or one pretty large retailer in France is ostensibly not abiding by it.
Darty.com says that you can only return an item if it can be resold as new. Basically, you may only open it to inspect it. If there are signs of use, you won't get the full refund.
Other retailers, like Amazon, may not care about this and refund fully no questions asked. But in my experience, Amazon is pretty unique in doing this.
>If you bought a product or a service online or outside of a shop (by telephone, mail order, from a door-to-door salesperson), you also have the right to cancel and return your order within 14 days, for any reason and without a justification.
In my experience, all retailers (have not tried in France, though) follow this law.
I think the issue turns around the "any reason" part. It doesn't say anything about the condition of the item, which, in my opinion, is the crux of the issue.
Unfortunately, I only have French references. The actual French law is at [0]. It says that the buyer is on the hook for any depreciation resulting from handling, apart from what is necessary to determine the characteristics and good working condition of the goods. So opening the vacuum box to see that it's not missing a part or something is fine. Vacuuming your house for 2 weeks is probably not. "Determine the characteristics" is ambiguous to me, so it's not clear where the line is.
For example, Zalando, an online clothes retailer, will accept returns for garments that have been "tried on" but not "worn" [1].
LDLC, an online electronics retailer, will accept returns for items in "original condition and packaging". I expect that if I buy a mouse, use it for a week and there are marks on the pads, they won't accept the return. [2]
Darty.com says that you can only return an item if it can be resold as new. Basically, you may only open it to inspect it. If there are signs of use, you won't get the full refund.
Other retailers, like Amazon, may not care about this and refund fully no questions asked. But in my experience, Amazon is pretty unique in doing this.