Is it permissible to use tawriyah (deliberate ambiguity) when exchanging merchandise that appears to be used, knowing that the store's policies do not allow exchanging merchandise unless it is sound?

It is not permissible to use equivocation if it leads to taking what is not rightfully one's own. So, if a buyer forfeits their right to return merchandise—for instance, by using it after becoming aware of a defect—then it is not permissible for them to use equivocation to make the shop owner believe that they have not used it.