I couldn't say the same of any Chinese ebike parts supplier.
I only work with the largest Chinese manufacturers - so I can only tell you about how service and backup is organised within our supply chain.
1. We hold stock of spares in Southend.
2. Under warranty: straightforward replacement of the whole item if used less than a month, straightforward replacement of sub-assembly (LCD, motor, controller, cableset) within guarantee period. Outside the guarantee period: we make a judgement on whether the item was sub-standard in the first place, if it is, we simply replace it.
We always prioritise service over sale, that is why when stock is low, we turn off the affected item from the online shop and ask customers to ring if they need to buy the item urgently for their project. We then make a judgement on whether we can spare a unit and still keep the service going.
3. All the faulty items are sent back to the factories and usually replaced with new.
4. If we have any technical query that we cannot answer, we email the factory and get a solution usually in a week a two.
That's why I have programmers for the controllers and so on.
There is no mystery. Chinese factories are just as straightforward to deal with as you would expect from any large producers in the EU. We translate and augment their manuals with our input and keep all manuals online
here.
I don't think the quality of service of Chinese motors, controllers, cablesets, LCDs is any less good than what you would get from European producers, except that we hold a few percents of stock for service to avoid delay. Better still, you can buy spares if you have to.