First,you should to connect the large range of companies which you can. You should notice that do not enquire the price of all the prodcuts and ask for samples at the first time,it won't be a wise action of professional importer.
Step2
Second,you can discuss the products which you request,talking about the specification and the usage of it.This process will help you to learn more about the exporter.
Step3
Third,if that your partner which you contacted is professional in your field across your validated, you can buy some samples from his company.Do not ask for samples for free,atless you should pay for the cost of delivery.
Step4
Fourth,you can order a little quantity of prodcuts,the quality control is very important,but most of factory can not be control it well. I recommand you that you had better to find a international trade company,beacuse they realize the situation of chinese factory.