Alibaba itself is legit, but it's more a middleman. I gambled recently and ordered through it, worked out fine. Sure, what I got was knockoffs, but I knew that going in. MOQs are what will hit you in the end. If you want to buy the non-knock-offs they're there too, but the MOQs are way too large for most regular consumers. My shipping cost about what it costs to order from the US for a package that weight, and got here faster than equal priced USPS shipping, so I can't say anything bad about it.
As whiterabbit says: Buyer beware. There's a lot of scams running.