Need Advice - custome product ( managing oversea manufature )

Hi! I'm new to all this so I'm unsure of what are the services and channels that are available to help me. I had some problems with the chine manufacture mostly in producing good quality checked product. Usually the sample/ prototype they made are good, but when it comes to production, about 30% ~ 40% of the product will have flaws. We have to do our own QC and pick out the once that cant be sold. My question is if there is a better workflow to this? Engage other company to manage the production and QC of the product? Is there any service that help you source out manufacture and also manage the oversea production?
Please advice. Thanks !