I bought some Tepe interdental brushes for my mum from the rainforest but her dentist told her she needs a different gauge brush, so I need to return these. As the package hasn't been opened, is it ok to mark it 'return to sender' and just stick it back in the letterbox, so I can be a cheapskate and save on return postage? Or, is that risky and it should be returned recorded delivery? It's only £12 of brushes.