The easiest way I think you can look at it is to compare DH Gate to Google.
If you want to find information, you search on Google, but the results you find are related to Google itself, Google is just the search engine you used to find them
DG Gate is what's called a B2B (business to business) directory. What they do is provide a directory for independent suppliers to list their services in.
This makes it easy for customers because they can find a broad selection of suppliers all on the one location, and of course good for the suppliers to list there because of the traffic flow such a directory creates.
So when dealing with a supplier that you find on the site, you have to remember that you are dealing with them, not actually with DH Gate, that's just the directory you searched to find the supplier.
Now you will find plenty written about DH Gate through the forum, but given that you are doing business with an independent supplier, not DH Gate themselves, you need to do all the security checks to make sure they are legit.
Just because they are listed on DH Gate, doesn't automatically mean they are a legit business, and b2b directories like these attract plenty of scammers looking to take advantage of the heavy traffic flow.