In Serbia, there are some agencies which help to find a job in China. Are there scammers between these agencies? 

Hi Goranko, there are TONS of agencies to help you find a job in China. I'm sure there are local Serbians who have connections to schools in China.

Two things you will think about:

1. How to tell if an agency is a scam?

2. How to tell if the school they are recruiting me for will be good to me?

My advice for both those questions is:

1. Ask for contact information for two their current teachers who are abroad. If they don't provide it promptly, that is a red flag. Talk to those teachers and ask about their experience with that agency. An agency that doesn't allow you to speak to their previous clients seems like it's hiding something.

2. Ask for contact information for 1 teacher currently at the school they are recruiting you for. If they don't provide it, that's a red flag. However, you should have already interviewed with the school and the school should be interested in you, because the school (and agency) doesn't want to waste the time of their current staff unless they want to hire you. But ALWAYS speak to one or two teachers at the school before accepting a contract.

Hope that helps!