Potentially there may be a claim against you for negligence because you should test products or ask clients if they have any allergic reactions. If it were me and to prevent any claim against you, I would offer a refund. If you do not then they may issue a claim against you for negligence and I do not know whether or not you have business insurance and therefore be covered. In reality this is a commercial decision for you to make, but if it were me, I would.
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