As far as I know, many vendors (I know MadVapes does it) buy bulk amount of high
nic/zero nic eliquid of the same flavor and mix them into a variety of nic strengths.
For example, if you mix 500ml of 50mg with 500ml of 0mg of the same flavor, you get 1000ml of 25mg of that flavor. If you have 100 empty 10ml bottles, you could sell them individually. Buying 2x 500ml bottles is way cheaper than buying 100x 10ml bottles.
The catch is that the liquid is not homogeneous, so some bottles might (and probably will) taste different from other bottles in the same batch, hence, funky tastes. There is no way of mixing them unless you have mixing machines that Dekang has in their factory.
So if the vendor is mixing eliquids, he could be buying straight from Dekang, cutting it, and there would be no way of telling if its real Dekang or not.
Just my two cents...