Brand new item sent back as used?

Hi all,

I’m pretty new at selling on Amazon and just received a return. I sent out brand new in box, factory sealed vibrating foam roller. The buyer selected return reason as “Item defective or doesn’t work” and their comment said “Not hard enough”. I’m not sure if they’re talking about the foam or the vibration, but when I received it it was open box and used, but not defective at all.

I’m guessing it was probably buyer’s remorse or she found it cheaper elsewhere. But now that it’s been used, I’ll probably only get like 50% of the brand new price selling it as used.

Should I be charging a 50% restocking fee or something? Let Amazon refund them and file a Safe-T claim?

It’s my first time dealing with this so any help would be appreciated. Thank you!