Semi-famous actors (often people who've done a lot of commercials or character roles), writers and agents/managers with varying levels of scruples keep certain arts-themed publications filled with ads, week after week, promising to tell you the secrets... if you pay for their seminar, service or book. In fact, preying on the "wannabe" is a cottage industry in any field that puts up barriers to entry, be it the movies or publishing or the music industry. We look at these people much like the get-rich-quick gurus on late-night TV... it stands to reason that they make more money telling you how to get rich with their secrets than they do using them, otherwise they'd be too busy using them to have time to sell them to you for $49.95.
The best advice we can give you are these few points...
Don't quit your day job. It can take years and you'll need money to live. Harrison Ford quit acting and worked in construction for a few years before coming back and getting his break. Bruce Willis was a waiter and bartender while he tried to get stage work in New York. Even people who seem to be overnight sensations played bit parts and struggled before they suddenly burst onto the scene in a prominent role.
A real agent or manager will not ask you for money (be it an "up-front fee" or "seed money"). They make money when they get you a job. Also, in California, talent agents must be licensed and there are laws governing their relationship with clients. Go to the unions, preferably SAG (Screen Actors Guild) or AFTRA (American Federation of Radio and Television Artists) or WGA (Writers Guild of America), and ask for their "franchised agency" list. You can buy it for a nominal fee or in some cases get it online for free. These lists will contain licensed agents who have signed contracts with the unions to follow specific rules when representing clients.
Take classes. It may be hard figuring out whether the $10 per session class is as good as the $100 per session class, and we can't help you there, but classes give you two benefits. First, they help you hone and perfect your craft, whatever branch of show biz you want to be in. Second, they will help flesh out a weak resume. If you don't have credits, you need classes. If you're wondering about the credits of the person teaching the class, look them up in our database. Except for writers on individual TV show episodes, we keep pretty good records.
Until you're commanding $20 million per film, you're not entitled to have a big ego. Don't reject parts you think are too small or insignificant because you're too busy looking for your big break. Judi Dench won an Oscar for six minutes of screen time.