I know this is basically preaching to the choir at this point, but it's summer and the scammers are out of hibernation.
They come up to you claiming they're from France or Germany, and pretend that they don't have any cash and ask for some in return for a bank transfer, that surprise surprise will never show up.
They got super agressive when I confronted them hustling someone, the man was right up in my face asking whether I had a problem, and the woman actually ran up and put her hands on me and tried to shove me after she realised she was not going to make any easy money. She then started fuming and tried to insult me which didn't really bother me because she looked like a cave troll...
Also if you're in the library be extra mindful of your belongings when you leave to go for a break, there are some people waiting to snatch your stuff the second you're away!