Hobbyking have the best and I mean the best customer service in the business. Fill out the necessary form and bobs your uncle. As with any company that sources from china the QA is not top notch but in hobbykings case they go the extra mile to make sure that the customer is happy.
They also address each issue and correct it.
For example;
I bought 2 sk8 motors from them when they were brand new to the store. One had a catastrophic bearing fail and the other had a dead sensor pcb. Quick back and forth with customer service and they asked for photographic evidence. Once provided they sent out the new units. They then sent me a credit to send the old ones back. Not for proof but for examination to correct the issues and with a proviso that if the new ones went bad they would replace free of charge with the improved versions. The new units worked a treat and still do.
I don’t run sensors anymore so moved to the sk3’s after hours of research and they have served me well.
Don’t be discouraged by one bad unit. The sk3 is still the most reliable motor you can buy atm.