The second car (or used car) market in China is not quite developed yet, for many reasons, such as the car market is relatively new, and not too many used cars are sold since Chinese do prefer new cars.

I do not know of any from previous expoerience to be able to recommend them, but two are:

http://www.justgoodcars.com/used-cars/cn-country/china/

http://www.cycusedcar.com/

if you can reach them.

If you are seriously looking for a good used car, I suggest you tell coworkers and friends to be on the look out for you, and let you know if they hear of any that will be sold among their aquaintances.  Check also with car dealers in your area to get an idea of prices, check other websites like eChinacities on their vehicles for sale in your city, place an add so anyone can contact you.  And above all, be patient, and double check car condition before committing to purchase

that first link, after choosing guangdong - dongguan- dongcheng, gave me a car for ssale in colchester UK???

https://www.nbcnews.com/mach/video/this-personal-flying-vehicle-is-ready-for-take-off-1289334339790?v=raila&