Real estate dos and don'ts (Beijing)

Hi guys!

I have a question for y'all;

What is the usual etiquette when dealing with real estate agents, can you be limited to only one company or can you deal with two agents at the same time?

I am having some problems with a particular agency and would like to perhaps explore a different agency, but still keep the other one just as a back up plan.

Is it normal to have two or more agencies?

Thanks

Naj