I have also worked for SFSC and I completely agree with what FedEx, Volvo and Isawitall said.
I didn't last long there cause I don't know how to remain quiet upon seeing someone being treated bad. Every time and everywhere, both in China and in Mexico, where I am from, if I see shit happening I have to raise my voice.
With Bill, I came here for a summer, no promises to work for longer or anything, and under a promise of "the boss" of helping me extend my visa for a month, since I already had a good offer in the south, but I wouldn't make it till the starting date with my then current visa. Since I was working per hour, I got a good deal the first week, cut half the second week, the third week only 4 hours (yes!! 4 f... hours, who can live on that??) But no complains about my situation cause I was expecting a favor with my visa. Nevertheless, I started talking to other teachers about theirs and my situation, looking for alternatives.
Anyway, since I arrived, I started noticing how other people would be treated different because of their color, nationality or political importance to the company. I have to make emphasis here on two things I hate about chinese way of doing things in respect to english schools: First, the boss will think we need them; they will have this idea that we are in china because we have nothing better to do or cause we couldn't get a better paid job on our own country. Second: If you do your job well, you will be rewarded with MORE things to do and the same salary!! Sweet, huh?
Well, while some teachers were being forced to exhaustion, others like myself would have to bargain the teaching time, despite the opinion of the students.
Making the story short, the visa process took more than 5 weeks, time after which I was told he had to bribe government officials to get it fixed, without my consent, and getting it updated to working visa for a year, instead of just a one month tourist or business visa as requested, and so, I had to work for him, under his conditions, that were half the salary I would have gotten in the south, and he would refuse to give me my passport back and laughed upon my warning of contacting my embassy, and they keep a copy of the text messages of communication with "the boss".
I like the people in this city. I know nobody on the other place where I was going, and I didn't come to china expecting to get rich and I was promised an apt for myself, so I stayed, but I did contact my embassy, and started taking note of everything happening in SFSC.
Not even a week later, I'm told a new teacher will soon move with me. 7 times did they go into my apt without informing me of it, finding me half nude a couple of times, despite I had complained and requested to be told when someone was coming. Can you imagine go out, come back and find your place different than how you left it? can you picture that 7 times in 3 days?
Well, I took all my stuff and moved to another apt with a friend, somewhere where Bill and his goonies could not reach. But I kept working punctually every day.
Result: I got fired!!
This "boss" will always play two faces, sometimes he will pretend to be your best friend, and then, if he gets to fool you, will change his version and screw you.
I got my passport back when he was trying to get me back to his school, cause he knew some other teachers would end their contracts and he would need someone to replace them. Too late.
This people should learn to think first and talk later.

I still have friends in trouble there. He just fired another friend after inviting him from his country and making work illegally (he never processed my friend's working visa), threatened some other friends to make them or other teachers stay, and still keeps my foreign expert certificate among other stuff belonging to other teachers who have worked in this place.
BTW, I know a couple of the teachers performing a midnight run, and I know there are lots of them.
New comers, I would really warn you to think it 3 times before coming to this place. If your need is not much, and you can look for something else, do it.
Since I am not using a nickname, I certainly expect consequences upon this post. I will keep you up to date if something happens.
Good luck and enjoy China. There is still lots of good things in this country.