Chinese visa in Vietnam

I have heard different things from different agents. One said a foreigner can't apply from afar - they have to go directly to the embassy (and I don't live in HCM or Hanoi). Another said I could, but it would only allow a stay for 20 days although the validity is 30 days (and it would still cost $185!). As the embassies are not very responsive, it is hard to get accurate information here. Do you happen to know more about this?