Imagine you are a vendor. A person walks into your shop with a magic sword to sell. You look at it, and tell the person you'll give 100 gold for it. The person looks at you, mutters a few magic words at you (charm spell) and you find yourself liking that person alot more, and you gladly say you'll give 150 gold for that sword....
Haha, need a little more realism here! No reasonable city would allow that kind of thing to be legal.
However, casting spells upon yourself to boost your personality/speechcraft/etc could be ok. And, of course if you cast that charm spell on the person while being stealthy and the person didn't see you do it, then sure, no crime to report to the authorities....
At the very least, shop owners, city officials, etc should have some sort of protection set up to prevent themselves from being charmed. Maybe a permanent charm detection or dispel in the area.