I think they can use their discretion in determining whether an item can be forwarder. Someone I personally know managed to get button batteries approved.

I'm also not sure if Google translate is working properly or not for some people, which may explain some bizzare posts lately. I would check that the warehouse is referring to liquid and not a magnet. Although it could also be a magnetic liquid... In either case, you'll need to craft up some reasons why you believe it should be allowed.

I think something along the lines that it isn't a strong rare earth magnet. (in that it won't interfere with the plane) That you believe if it is a liquid, that it will stay intact throughout the flight. (cough, if you have bought cheap pens and fly regularly, you'll know sometimes they leak/explode).

Of course these might not be the underlying reasons why China Post has decided it is not alright to ship these materials.

However, if it does get approved you aren't out of the clear yet. For example if you buy batteries on aliexpress posted via China Post Air; usually the seller will just try post it anyway regardless of the regulation and if it gets stopped then the seller sends again at their own cost. I had one instance where some 9v batteries were confiscated. Furthermore, I'm not sure if the taobao warehouse will put it through a more sensitive channel or not, but if you aren't paying any extra, then I suspect it will be hit and miss when it comes to getting it past customs; you might need to pay the shipping fee again if it gets sent back to the warehouse. From what I've personally experienced on aliexpress, it is possible the item may be destroyed depending on how serious the offence was to make people comply with what is allowed to be shipped.

The method isn't without risk, unless of course the item is 100% not on the prohibited list. I've also seen some with off-white items stopped at customs; which from some of the pics here seems to be a common item allowed by the warehouses; oddly enough.