T., Vietnamese American:
My experiences with ethnic Chinese in Vietnam were largely negative. I found that they were generally more cut-throat than the natives when it comes to business. There just seemed to be more Chinese who were unscrupulous about eliminating their competition. After I migrated to the US, the East Asians I met here did not give me much reason to change my impression. People from Korea and China I encountered in the US both have a tendency to be nice to you when they need something from you, but once they are done using you, they discard you rudely. From my experience, East Asians are generally more manipulative than Southeast Asians. There are of course, some honest exceptions, one of them being my friend, who is ethnic Chinese, but not from East Asia. Maybe the fact she wasn't raised there makes her different.
I know some of the East Asians, especially Koreans and Japanese, look down on Southeast Asians because we have darker skin. They can pay lip service to Southeast Asian cuisine, arts, and even ogle our women, but they don't really respect us on an equal footing.
In Singapore, there is a widespread perception that a higher percentage of Chinese business people tend to be dishonest - they charge more for less, compared to be natives. Even Chinese people admit it is the case. But perhaps it is an immigrant thing more than a 'race' thing. Indians too, are seen as cunning business people who overcharge.