Buying From Alibaba and Other Chinese Wholesalers

Go by reviews and their stats

Look for their earned badges first, next to their company names and check if it is valid or not and how long they are trading with the website like Alibaba.com before you look at their products in details. Make sure they are the manufacturer of the product and not an middle man ( if you want to get it for even cheaper price ). Also take a time to read through the site so you know what is the badges means. Then, ask them the questions, as much you can about the product in detail to see if they have the knowledge of the product that they try to sell.
I would personally recommend to deal with suppliers or Manufacturers who has the following badges and requirements: Years with Alibaba (Minimum 3years), Gold Members or not and most importantly are they been Audited by Alibaba and are they holding the valid Certificate or not. Serious Manufacturers and suppliers will have the above things i mentioned as they know the value of it. In this way you can be safe at least 99%!
I hope this helps! If you want more details drop me line hear.

Trial and error. Those reviews are misleading. Its just like purchasing in the US. If the price seems too good to be true it probably is. You can read other peoples reviews but be careful. Most those sites do not show what the people bought to place a review on.