Great thread Richelle! I've used sellers on DHGate, Aliexpress and Alibaba. I've found them all hit and miss: Sometimes the products and customer service were good, sometimes they weren't.
In one instance, I bought around $2000 worth of stock from a seller on DH Gate and when it arrived, it wasn't as high quality as I was expecting. It wasn't poor enough to demand a refund, just not up to my own standards for products I was proud to sell to my friends and family (my rule of thumb I live by when selling products). In other cases, I've bought great items that I've re-sold for good profits.
I've also bought personal items from some of these sites.
Another one I would add is eBay.com. I've bought wholesale lots from eBay and marked up the prices by 500% and made a lot of sales!
I've never personally been ripped off by these sites because I do my due diligence and research the supplier as much as possible before I purchase from them, but I know a LOT of people who have been ripped off on these sites, so it pays to take Richelle's advice and pay with safe payment methods such as PayPal, Escrow and credit card.