I know individual vendors will vary but is the system robust enough to prevent pure fraud?
.[/quote]
Short answer; no not really.
I have bought over 160 times from them, over several years, with usually very good experiences.
I have mostly kept it to cheap stuff; clothes, cheap electronics, kids toys, camping gear.
Shipping, as others have said, is all over the place: 6 days to 6 months (Usually 12-20 days).
OTOH,I usually take a "free shipping" option, and I suspect subsidised shipping is one way that the Chinese government supports its industry. I have bought lots of products shipped from China for a total cost less than postage would be from the other side of town (say, an iPhone case or power cord for $2 - 3 including delivery).
The more expensive the item, however, the more chance of it not showing up, and I have had a couple of bad experiences there. The AliExpress "buyers guarantee" is ultimately useless.
What happens is your (say) $100 external hard drive fails to show up. You lodge a dispute.
You then receive a Chiniglsh request that you provide your documentation proving that you did not receive your goods.
You reply: "To what documentation do you refer? No documentation is produced for a good that is not delivered."
They reply: "No documentation. So sorry, we have released your payment to the seller"
You contact Visa, who uphold your dispute, refund you, and go to battle with AliExpress (for the 10 millionth time, I'd guess).
Aliexpress send you a rude note expressing their disappointment, but nothing else happens.
If you can put up with that kind of pain in the A, 98% of the time you get some decent Chinese junk, cheap.
I'd like to see how you go with a $350 bit of kit. I'm tempted to buy a new pool heater that is about 20% of the domestic price on AliExpress/ Alibaba, but I don't know if I'm confident enough.