Tesco (a supermarket in the UK) employees do that sometimes. You get loyalty points when you shop over there. They are supposed to ask you if you have your clubcard. This is scanned before you are billed for the items you have purchased and you are supposed to get the points credited to your clubcard account.

If you say that you dont have a clubcard, I have seen employees scanning other cards(Could be their own!!!). Obviously this is not company policy to scan a dummy card as not all of them do it!!!