In Europe you have 14 days to return a device if you have bought it online. It can be opened, no fee should be applied (some can ask for delivery fee but at the end they should return that $ too). The idea is very simple, if you order a device online, you lose the ability to check the device the same way you can check it when you are in a shop and can look at the demo device etc.. So those 14 days are meant specifically to let you open and check the device and if it meets your standards jsut stay with it or send back. Ofc it is a hustle for any seller so they do whatever they can to make you stressed about returning the device (like saying that they accept only unpacked devices etc) but it is your consumer law protected by government.
PS. Like common trick big shops do here is if you order online they still push you into picking it up at the shop. This way they get rid of the 14days rule bc by law you could check the device when picking up at the shop.
Keep in mind that 14 rule pushed people to buy online bc thanks to it we actuall get rid of any anxiety when ordering blindly something new. So even if a seller is losing money on a return back delivery, he sells 10 moe devices thanks to others ordering the stuff bc of the possible ruturn even if they are not using it. So overall it is a win-win situation.
Ofc if you damage the device or wear it significantly and in a way it is far beyond what normal use would do, they can reject your return.