This happened to me today. I had gone shopping and left my helmet in the place earmarked for that. After shopping when I came back to find my helmet, I could not find it. Instead on the rack I found another helmet of the same brand, only much older and uglier. (His also had some ugly stuff written on the back and had tinted glass) Now, on the way back home I did not even want to wear this helmet. The shopkeeper did not want to take responsibility either and had not noticed who took the helmet. (Wow!!)
Now whether the person mistook it for his helmet by accident or purposely took my new helmet, I do not know. I however left my phone number with the shopkeeper just in case this guy comes along and honestly returns the helmet.
I have decided that the person who took my helmet is either (a) really dumb for having mistaken my new helmet for his old helmet (I would say brain dead if he does not return the helmet) or he is (b) a proper thief (I shall use better and filthier language if I am not contacted in a few days)