I also got bad experiences with DUC service department in Hanoi. I am not sure about Duc service dept in Ho Chi Minh city, although I heard its mechanics are much better.
I bought a Hyperstrada from Hanoi DUC dealer in Dec last year and experienced engine stalls a couples of time, in the first 1000 km. I did some research in this forum, and I found that some Hyperstrada owners also have the same problems. Most of them got the problems fixed by updating the ECU at the dealers.
I brought it in last week, at that time the mechanic (his name is Đức) couldn't tell how it could happen or what he could do to fix the problems, so I showed him the thread from this forum suggesting about ECU update. Two days later he called me and said the reason might be poor quality petrol and all what he could do was to add a bottle of fuel additive (produced by Yamaha Vietnam) to the petrol.
After I came to collect my bike and drove it home, I realised that the bike had such a strange engine sounds and it somewhat lost its robustness. But the worst thing was my customised Ducabike handle clamp and pump protector were damaged and the carbon fiber inlays were missing. I called Đức, but he insisted that the Ducabike stuffs were untouched during service process. He denied any wrong doings of himself or his colleagues, but passed all problems to my side saying that I accidentally peeled the carbon inlays off when I washed my bike with high pressure water pump!
Unlucky for him and lucky for me, two days before when my bike was still in the service dept, a guy in the DUC Hanoi sale department took some photos of my bike and posted them in his Facebook (he already added me as friend). The photos showed both of customised parts still had the carbon inlays on them. So those photos are my proofs. I talked to DUC hanoi manager and she accepted the faults and said that they would order the new parts and replace them for me, but she couldn't say when. I asked her for a report, with signatures of witnesses, but she refused.
Sorry for long talking, but DUC Hanoi has shown no professionalism to customers at all. Its mechanics are incompetent, irresponsible, unhonest and collusive.