Also, when you charge someone else's credit card with an amount exceeding the actual amount then giving back some portion with cash, it is actually the same as using credit card's cash advance service, but no interest, that is why credit card company will punish anyone who does this, because usually the interest for cash advance is pretty high.

I used to be a waiter in a restaurant and once there was a customer asked me if I could charge $50 more on his credit card then gave him $45 back leaving the $5 as tip, my boss told me to refuse, because it was an illegal cash advance and the credit card company would fine the restaurant, not the customer.