If you are employed by a school, and subsequently they don't like you, you can be fired. But if you're workin at a school through an agent, there's less chance of being fired, as the school doesn't know how to hire foreign teachers direct or chooses not to do so. Chances are working through an agent is more secure. and they'll get you a visa and protect you. It's in their interests to do so, and the school too. As for China, the culture allows for foreigners to work with visas as long as they're not expired. I've done it too, no prob, are you a man or a mouse?