In order to find a good supplier (no matter if t’s Alibaba or other channels), I suggest carefully checking their history.
Nowadays, you can easily find information about almost every business, so once you see a supplier that you like, do some more digging about him, try to find his own online stores or other sellers that sell his products and check their feedbacks.
If you see that the products consistently get good feedback, that means he is legit.
A legit supplier will also be willing to give you more information about himself, since he will be interested in having more resellers (unless he already has too many and cannot keep up with the order rate, but that’s rare since you always want to grow and make more money).
To summarize, just try to find as much information as you can about the supplier and the quality of products he sells, you can also order one sample and test it yourself.
For further reading, check out this great step-by-step guide for finding reliable suppliers: Sourcing Reliable Suppliers for Your eBay Business | CrazyLister