If you’re a student considering a career as an actor (or if you’re a teacher with students considering an acting career) you must follow The Gigsmacked Blog.
They just posted a vitally important laundry list of what to be aware of when you’re looking for an agent. (“Sounds Too Good to be True? Agent Scams and How to Avoid Them“)
I was very lucky that I was never scammed this way, but I’ve come across all sorts of people who were. The vast majority ended up without a single job, without a single audition, and thousands of dollars poorer.
The simple rule of thumb is this: An agent should only be making money when you make money.