why some Vietnam clients take Chinese products as lower quality products?

I met some question from my partner that:

why some Vietnam clients take Chinese products as lower quality products?
or
Why some Chinese products in certain country are taken as bad quality or lower quality?
or 
Made in China roots blower are bad quality.

We are top roots blower, air blower, vacuum pump and turbo blower manufacturer in China, but we seldom sell the Vietnam except some big projects, as big projects need big blowers and they care about quality, only few manufacturer can meet their requirement, for example big Vietnam group  Hoa Phat Steel – Tập đoàn Hòa Phát, they bought a lot from us for their own projects since year 2011.

I had a meeting with one big engineering company in Ho Chi Minh city, Vietnam last week and was told that some end user are concerned about some Chinese brand air blower, so i explained to him about how is this happened. China is different from some US and EU countries, when we list the roots blower manufacturer in US and EU, we found that quite few brands there, AERZEN, PEDRO GIL, ATLAS, HIBON, ROBUSCHI in EU and GD, DRESSER, TUTHILL etc, total less than 20 manufacturer in EU and US based on population of 1 billion. why this happened? because low quality manufacturer is bankrupt with time and only good quality factories left. Do you know how many roots blower manufacturer in China? more than 100 air blower manufacturer based on 1.4 billion population. and China is on the stage of eliminating low quality manufacturer. And i arranged meeting with most biggest Vietnam importer in Ho Chi Minh City and Honoi city, we are TOP MANUFACTURER in China and i quoted satisfactory price based on our quality, they always bargain more than 20% discount, how could we have so high profit based on satisfactory price and high quality? Normally we couldn't reach an agreement. But i believe they found supplier based on their target price, obvious that quality is not satisfactory and hurt the end user finally. Trust me, if you work with branded manufacturer with advanced CNC machining capacity, never worry about quality and service, they care about their reputation more than any others.