Sorry, I wholeheartedly disagree with you here, MathNut.
Your questions focus on whether ownership is transferred, but that's not what's relevant. What's relevant is use , and Swiss law (and that of most civilized nations) states plainly that items sold must be new and not defective, unless labeled otherwise. If a store marks something down because of a defect (and yes, this gets caught in the stores on new items all the time, either from employees restocking or because a customer points it out), there is nonetheless no reason to expect it to be used. (Swiss case law also says that it's not considered "use" to open a box to inspect an item, so you can order something by mail, open the box, look at it, and still have it count as unused.)
So basically, unless you go to a Brockenhaus or a used car dealer, items sold without being marked as "used" must be new. Any store doing anything to the contrary is breaking the law.
(N.b.: Swiss law provides no provision for non-defective returns whatsoever. If a merchant chooses to allow it, it is as a courtesy and thus may be encumbered with whatever conditions the merchant wants. What a merchant may not do, for unused goods, is to eliminate the warranty. They can -- if they tell you before the purchase -- reduce your options for remedy, e.g. "attempt repair first" or "no refund, replacement only". But ONLY if they told you in advance. Such a restriction printed on the back of the receipt means nothing, because you don't see it in advance. A sign by the register does count, though.)
Having worked (non-clothing) retail, you sometimes have to guess if a customer is lying when returning "unused" goods. There were definitely instances where a customer told me something was unused and I could plainly see that it wasn't, but it being within the return period, I had no reason to deny the return -- I just processed it as a used return in the computer. (That also meant it didn't go back on the shelf.) When in doubt, I did it as a used return, because you didn't want used stuff to get sold, as happened to the customer after the OP.
What I don't understand is why the shopkeeper would resell it. In chain stores, defective merchandise normally gets either written off as damaged, or goes back to the manufacturer -- either way, normally not something that dings the manager.
I've heard that some clothing stores categorically do not resell returned clothing. They write it off (easy to do when the cost of goods is 5% of what you're selling it for...) and either trash it or donate it.
This is of course why clothing has tags on it that wildly exceed what is necessary to hold a price tag: They put artificially large and uncomfortable tags on them to force you to remove the tags to wear it, creating a relatively reliable way of proving that you didn't wear the clothes.