free starbucks coffee

i accidentally found this method, not sure if its an actual method or coincidence but i purchased a coffee (frappe) and only had a $100 dollar bill...they said they couldn't break that and gave me the drink for free....i thought that was nice of them....few months later i went to get a coffee at another starbucks, was thinking the $100 trick would work, but only had $50 bill...gave it to them and they said they couldn't break it and gave me the drink free...not sure if it's just a coincidence or not, but worked for me!