I say no. Accidents are accidents; if you handed a valet a $100 tip instead of a $5 because it was dark out, you would prefer that he give it back to you.
If the business is large enough, they can eat the loss. Small businesses hurt more. Be considerate, everyone makes mistakes.
I would say it depends. If it was an expiring promo or something like that I would think good business Would be to honor it. If it was a flat out mistake then I say no.