I think this was said above.

Because the buyer pays all taxes/fees. Expect to be asked to provide two sales invoices. One for a lesser amount to reduce the tax/fees payable.
Yes this is illegal, but in Kunming it is prevalent.

Certificate of no impediment, I am not sure about. But here is what I had to do for my UK marriage certificate, using an agent.

The certificate was sent to the agent in the UK.
Agent then sent the certificate to the UK Chinese consulate in London.

The Chinese consulate then sent it, through consular channels, to the British Embassy in London.
The BE then had it officially verified and returned to the Chinese consulate, via consular channels.

The Chinese consulate then provided certification (green official certificate with holographic seal and red stamp).
Certified document sent to agent
Returned to me.

NB Certification in this case was only valid for 6 months.

Documents can be difficult and the rules seem to change from country to country. The rules can also change between countries, i.e. a Country A document in Country X can be treated differently to a Country B document in Country X.

I know this isn't helpful, but be prepared to give them what they ask for. And expect what they ask for to change.

The law will be ignored until they decide to have a crack down. These crackdowns only last a few weeks.

Ravi is perhaps a classic example of why non-native speakers with a dictionary are a liability.

My understanding.
As a non Chinese citizen you need to be part of a group to get the permit.

For a definitive answer, go to a travel agency and get them to get the travel permit for you.

I also believe that the answer can change depending on political sensitivity at the time. Travel permits have been known to be unavailable in the past.