I have three scripts under active consideration right now. If I sell any or all of them, my retirement will be essentially set! Selling a teleplay for an existing TV series won't quite do that, but it will bring a lot of income in the form of residual payments over the long term versus a single one time bigger payment for a screenplay. My agent works on both types of sales for me and get's 10% of everything, including residuals. In fact HE gets paid before I get paid and thats fine by me. Now I've only been a client for a short while and so he hasn't actually sold anything of mine, yet. But he's established and has been in business for over 20 years, so I remain hopeful just as I remain busy. All in all, I write for me not for the $$ it might bring. Still, it is an important possibility.
Thanks. Just wondered what it was like to be represented. Good luck.