Overall, we were disappointed at the quality of workmanship on samples. The quality of the zipper used was very poor, and one of the sample bags did not zip up well. The finishing of the top part for connecting the over shoulder strap was not nice and we decided to have our designer review. See other Articles on Sarobag Development.
Adapting an existing product is much easier than making a whole new design. The solution is to follow production of samples and orders on a daily/weekly basis as appropriate. Send staff in to quality control and make factory visits. Follow strict standards and explain your requirements to managers and where possible also to the workers on assembly lines in Mandarin Chinese.
You can see the poorly closing zip on our Sarobag sample below. If you want quality you have got to pay for it. The best known zip brand is YKK but there are a few zip companies in China which have very high quality zips also. Different zips can seriously affect cost of a bag, especially on bags like this where zip is extremely long.