Could you return a mouth guard without the receipt

Yes, for store credit, if unopened (would you buy an opened mouth guard?).

You cannot return anything without the receipt, however you are able to exchange if and I emphasize"IF" you are doing so for a legitimate reason.

No

Dont think so..but why do you not need a receipt?

Yes for store credit

Yes, if unopened for store credit no cash back.

I dont think so

Not if you've opened it.