Reading glasses can be exchanged or refunded at most stores if they are not suitable. I would hope the FDA specifies the same for OTC hearing aids.

Setting FDA requriemetns on return is example of overregulation that is frankly not needed - I struggle to come up with online/DTC brand that does not have free 30 days return policy. Virtually all electronics on Amazon has free return. This is pretty much industry standard.

But who does the "proper" tuning?