The chances of you purchasing a working Heng long tank on Ebay ( Or one which last longer than a couple of weeks) is about 50/50.
They are rubbish plain and simple.
If you want an RC tank that does what it says on the box and will last a life time, choose TAMIYA. They are worth saving up for.
Tamiya tanks (When well made) will hang on to their resale value also. Whereas Heng Long stuff is next to worthless (You'll pay more for the postage than for the tank.