People to avoid, Athens
The single male traveller will often be approached being offered help or being invited to a bar to make friends. More 'friends' and beautiful women will appear and they´ll eventually end up paying a huge bill at the bar.
I was approached twice in this manner but since I had already been informed about it I didn´t fall into this trap.
This one is for men. Men will enticed you to go to one of the bars or clubs(mostly likely strip joints) around Omonia. In the very least, they will charge you a fortune for drinks and worse; strippers pickpockets you or rob you. I was warned by the owner of my hotel. Surely enough, I was approached by one around the Temple of Olympian Zeus. These hustlers are very keen and read you like a book. They have props, in my case. Business cards of people from where I live. Anything to gain your confidence. I'll give these people an A+ for salesmanship.